The Daily Sign-Out

New IASLC classification of lung adenocarcinoma!

The February 2011 Journal of Thoracic Oncology has the long-awaited new classification for lung adenocarcinoma.  This paper is a MAJOR multidisciplinary achievement that aligns the interests, concerns, and expertise of pathologists, oncologists, surgeons, and radiologists.  I can't think of another classification in any other organ system that has attempted this kind of collaborative effort or produced an audacious result.  It is evidence-based and rationales for various critical decisions are clearly expounded.

One of the interesting asides is the questions posed by different specialty stakeholders.  Studying this alone provides compelling insights into different perspectives on lung adenocarcinoma.  As pathologists, we must appreciate and understand these perspectives to be effective participants in the care of these patients and remain relevant to the oncology team.  Thus, there is a radical shift from the previous paradigm tumor classification meant mainly for pathologists:

The goal is not only longer to solely provide the most accurate diagnosis but also to manage the tissue in a way that immunohistochemical and/or molecular studies can be performed to obtain predictive and prognostic data that will lead to improvement in patient outcomes.

Here's my key points:

• Modified classification scheme for small biopsy/cytology specimens (Table 2)
• Incorporation of histochemical stains (mucin), IHC stains (TTF-1, p63), and molecular studies in classification--reflecting what we already do in practice, I might add
• Elimination of "bronchioloalveolar carcinoma" and replacement with adenocarcinoma-in situ including a size limitation of ≤3 cm (and insistence on total histologic examination)
• Introduction of term/concept of "minimally invasive" ADC defined as a discrete solitary lesion ≤3 cm with predominantly lepidic growth and ≤ 5 mm invasion in greatest dimension
• Definition of a new subtype, "lepidic predominant" ADC (LPA) for nonmucinous tumors with a predominantly lepidic growth pattern but with at least one focus of invasion > 5 mm
• For invasive ADC, semiquantitative subtyping into patterns in 5% increments based on "comprehensive histologic subtyping"--this incorporates previous work of Dr. Travis et al (see previous post)
• Re-classification of "formerly" mucinous BAC as invasive mucinous ADC, in recognition that the majority of these tumors demonstrate invasion--Table 4 is a nice summary of invasive mucinous ADC versus nonmucinous AIS/LPA
• Addition of enteric ADC as a recognized variant--these are the tumors that morphologically (and immunohistochemically CK7-,CK20+) resemble primary/metastatic colorectal ADC
• Re: small biopsies--"All current data that justify the importance of the distinction between histologic types of NSCLC in patients with advanced lung cancer are based on light microscopy alone." (my emphasis)
• Clearly stated considerations for "good practice" regarding judicious use and conservation of small biopsy specimens
• Very helpful algorithm for ADC diagnosis in small biopsy/cytology specimens
• Excellent table (5) summarizes associations between ADC subtypes, molecular patterns and radiographic appearance

There is also a nice summary of research questions for specifically for pathologists as well as clinical research questions related to the identification of prognostic and predictive markers/features.

One recommendation that was made in consideration of future molecular research is one I think is applicable not only with regard to future molecular studies but is crucial for all studies looking for prognostic and predictive markers: that these studies be based on "well-annotated clinical and pathologic datasets."  My own personal experience with lung cancer research confirms this recommendation and I wholeheartedly agree.  It is essential to carefully review all cases included in any retrospective study and I would propose that a histologic tool be developed for annotating cases prospectively to be entered in a database.

 

Optimal panel for differentiating NSCLC in small specimens

There has been a plethora of papers, abstracts, and marketing materials in the last 12 to 18 months regarding the "optimal" panel for differentiating adenocarcinoma (ADC) from squamous cell carcinoma (SQC) in non-small cell lung cancer (NSCLC).  The December 2010 American Journal of Surgical Pathology features a paper from Terry, Leung, Laskin et al. that evaluates an optimal panel and, perhaps, more importantly, a testing algorithm for differentiating ADC from SQC in small biopsy specimens.

Caveat: one of the authors is the Medical Director/Chief Pathologist for a commercial pathology reference lab specializing in IHC diagnostics (PhenoPath Laboratories).

This study makes several practical points that can be nicely summarized as bullets:

• For ADC the most sensitive marker and best negative predictor is CK7: 93% sensitivity, 91% NPV.
• For ADC the most specific marker and best positive predictor is Napsin A: 94% specificity, 90% PPV.
• TTF-1 has similar specificity as Napsin A for ADC.
• For SQC the most sensitive marker and best negative predictor is p63: 84% sensitivity, 86% NPV.
• For SQC the most spepcific marker and best positive predictor is NTKR2 (a neurotrophic tyrosine kinase receptor, rarely used outside of research labs) but CK5/6 has a nearly identical specificity and PPV: about 95% specificity, about 95% PPV.
• No single marker is BOTH highly sensitive and specific for either ADC or SQC.

The authors identified a 6-marker panel that includes p63, TTF-1, CK5/6, CK7, Napsin A, and mucicarmine has demonstrating the best AUC in ROC analysis.  Since a 6-marker panel may not be feasible (or even possible) due to various factors with small specimens with limited diagnostic tumor material, the authors develped a binary scheme using a sequential addition of markers (Fig. 3, 1809).

The authors do point out, however, that the "best" sequential order may vary by laboratory according to the actual senstitivities and specificities acheived in individual labs and this is important to remember if your lab does not perform all of the stains.

I think one important caution, however, is to note that this study was performed using tissue microarrays derived from resected lung cancer specimens and did not study or validate the performance of these markers on "real" small biopsy specimens.  The authors claim that the results are "similar" to earlier studies using actual patient biopsy material.  Given their careful statement above regarding the "best" sequential order, I think that this is somewhat disingenuous elision over important details regarding significant differences between resected tumors and small biopsy specimens.  Notwithstanding this major issue, there are some good quantitative data here that warrants your consideration in evaluating your own panels at least for comparing your own sensitivity and specificity for individual markers.

Association between EGFR mutations and ERCC1 expression in NSCLC

Gandara and colleagues from UC Davis Cancer Center have published ahead-of-print on October 21, 2010 in Journal of Thoracic Oncology an interesting article examining the association between EGFR activating mutations and ERCC1 gene expression in NSCLC.

NSCLC tumors that show EGFR activating mutations are also more likely to show low expression of ERCC1 mRNA levels according to this study.  This might explain (at least in part) the clinical observation that suggest enhanced efficacy of platinum-based chemotherapy in patients with EGFR-mutant NSCLCs.

The authors performed microdissection of tumors from 1207 patients with NSCLC and analyzed EGFR mutation by allele-specific by PCR and ERCC1 mRNA expression by RT-PCR.

Median ERCC1 expression was histology-related: adenocarcinoma (ADC) showed a lower median expression (1.68 (0.22-11.31) versus squamous cell carcinoma (SQC) (2.42 (0.51-14.28) (p<0.001).  The presence of EGFR mutations was highly associated with low ERCC1 expression (p<0.001).

It would be interesting if future or additional work focused specifically on ADC as a subgroup and perhaps the authors might consider re-analyzing their data and presenting this data.  I suggest this as a practical concern since we are not routinely testing SQC for EGFR mutation.  In addition, the next step is to examine the relationship between EGFR mutation and low versus high ERCC1 expression and response to combined EGFR-TKI and platinum-based chemotherapy, especially in advanced stage disease.

ALK Inhibition in Non-Small Cell Lung Cancer and Inflammatory Myofibroblastic Tumor

Great stuff in this week's NEJM!

Today's (October 28, 2010) New England Journal of Medicine has no less than three articles reporting the use of small molecule ALK tyrosine kinase inhibitor crizotinib (PF-02341066, Pfizer) in non-small-cell lung cancers harboring the oncogenic fusion gene EML4-ALK and in a patient with ALK-rearrangement positive inflammatory myofibroblastic tumor, a distinctive but uncommon soft tissue neoplasm.  

Pathologists should be familiar with these articles--at least so you can suggest appropriate testing for ALK rearrangement but also that you might "shine" at your next Tumor Conference ; )  BTW, the article by Kwak et al. presents in paper form the data that rocked this past summer's ASCO Annual Meeting regarding crizotinib.

Of interest to pathologists is how the EML4-ALK rearrangements were identified.  Importantly, Kwak et al prospectively evaluated about 1500 NSCLC formalin-fixed, paraffin-embedded tumor samples by FISH using an ALK break-apart probe.  The study also included a retrospective analysis on the FISH-positive cases using RT-PCR for specific EML4-ALK fusions and immunohistochemistry using anti-ALK antibodies.  Note that the authors did not use ALK-rearrangement-specific antibodies that have recently become available.  Mino-Kenudson and colleagues recently reported their experience in Clinical Cancer Research using a highly sensitive antibody for ALK-rearrangement by IHC.  The availability of these mutation-specific antibodies could make IHC a preferred (and cheaper, more widely available) method for screening to replace FISH.

In this same issue, Choi and colleagues report report the discovery of two secondary mutations within the kinase domain of EML4-ALK in tumor cells isolated from a patient during the relapse phase of treatment with an ALK inhibitor that appear to confer resistance against two different ALK inhibitors (!).  Curiously, each mutation developed independently in subclones of the tumor.

Finally, Butrynski and colleagues report a sustained partial response to the crizotinib in a patient with an ALK-translocated inflammatory myofibroblastic tumor (IMT) indicating the biological role for ALK signaling in tumors with ALK rearrangement and a therapeutic strategy for crizotinib in ALK-rearranged IMTs.

Drs. Bengt Hallberg and Ruth Palmer provide an insightful editorial which should also be read (at a minimum).

Lepidic growth of articles about bronchioloalveolar carcinoma of lung (!)

Literally within minutes of publishing my previous post following up on a digital case challenge on bronchioloalveolar carcinoma (BAC) of the lung, I discover this month's (October 2010) Archives of Pathology and Laboratory Medicine on my desk which contains a nice article by Lindsay Schmidt and Jeffrey Myers titled, "Bronchioloalveolar Carcinoma and the Significance of Invasion: Predicting Biologic Behavior" (Arch Pathol Lab Med 2010;134:1450-1454).

The issue is how to designate tumors that show stromal invasion but are mostly BAC (think Miracle Max from The Princess Bride: "It just so happens that your friend here is only MOSTLY dead. There's a big difference between mostly dead and all dead.").  Ah, but how much is mostly?  This paper summarizes studies that demonstrate the presence of invasion only becomes important for prognosis only when the invasive component measures more than 0.5 cm in greatest dimension.  Unfortunately, the WHO Classification rather dogmatically defined BAC as a tumor showing "growth of the neoplastic cells along pre-existing alveolar structures without evidence of stromal, vascular or pleural invasion" yet enigmatically did not distinguish cytologic features as part of the diagnosis.  The authors discuss the alternative viewpoints to address this situation by either a new diagnostic term (microinvasive or minimally invasive adenocarcinoma) versus just revising the current definition of BAC to include those tumors with less than 0.5 cm of invasion.

A worthy pearl: 2 features most helpful in identifying invasion: (1) a myofibroblastic stromal response (distinguished from "alveolar collapse" and central scar) and (2) isolated tumor cells.

Check out the paper, I especially like the gross photographs.  I've seen worse.

Just for fun, check out Miracle Max:

 

Follow-up on Adenocarcinoma with BAC Features

My last post was a "Digital Case Challenge" presenting a case of pulmonary adenocarcinoma with non-mucinous bronchioloalveolar (BAC) features.

Here's my synopsis of 3 recent papers on bronchioloalveolar carcinoma that focus on the clinicopathological, histological, and molecular differences between the two subtypes, non-mucinous and mucinous, as well as the practical importance in distinguishing these two subtypes.

1.  Wislez et al, in a recently published paper in Lung Cancer (2010;68:185-191), studied 50 cases of non-resectable adenocarcinoma with bronchioloalveolar (ADC-BAC) features who were enrolled in a multicenter study to evaluate gefitinib as a first-line therapy for non-resectable ADC-BAC.  Previous trials (SWOG S0126 and IFCT0401) have shown that the mucinous subtype was associated with a lower response rate and was predictive for shorter survival after treatment with gefitinib.  The purpose of this study was to identify markers that would better characterize each subtype.  They first classified each tumor by routine H&E staining using conventional criteria.  They found that three variables enabled segregation of 96% of cases (48/50 patients): diastase-resistant PAS staining, IHC staining for TTF-1, and EGFR mutation/genomic gain.

dr-PAS: 80% non-mucinous ADC-BAC tumors showed <5% positive cells; 83% mucinous ADC-BAC >5%

TTF-1: 95% non-mucinous ADC-BAC express TTF-1 >20% of cells; only 27% mucinous ADC-BAC

EGFR mutations (exons 18-21): only 3/25 (12%) in non-mucinous ADC-BAC but none in mucinous ADC-BAC

The last findings are lower than previously published rates for non-mucinous ADC-BAC in both Asian and U.S./European studies.  Moreover, EGFR exon 18-21 mutations have been reported in mucinous ADC-BAC, albeit at a much lower rate compared to non-mucinous subtype.  Which leads me to a second recent report I recently reviewed.

2.  Casali et al (J Thorac Oncol 2010;5:830:836) presented a single-institution retrospective study from Italy of 40 cases of BAC based on strict application of the 2004 WHO histologic classification of BAC (although 6 cases were not completely sampled for histology due to large size/pneumonic involvement).  Their purpose was to compare previous studies of BAC in  primarily Japanese/East Asian studies with their exclusively European Caucasian patient population.  Their findings are similar but not identical to these previous studies.  Non-mucinous BAC presents more frequently as a solitary mass and early stage (cf. mucinous subtype), whilst mucinous BAC more frequently presents as multifocal tumor or a pneumonic pattern of lung involvement and in more advanced stage.

The overall incidence of EGFR mutation was similar to the study by Wislez et al (17%) which is also less frequent than that reported in primarily Japanese reports; they did confirm a strong correlation with never-smoking status and female gender.  Also, they found a significant difference in mutation profile between subtypes: 6/14 non-mucinous BAC versus none in mucinous BAC.  Conversely, KRAS mutation was found in 12/13 mucinous BAC versus 3/20 non-mucinous BAC.

Although this is a small, single-institution study, there is helpful and interesting survival data that shows significantly increased OS and RFS for non-mucinous versus mucinous/mixed BAC in early stage (IA and IB) tumors.  They also note the raw numbers for the small subgroup of patients with multifocal tumor (N=6) and pneumonic involvement (N=7) which suggest a dismal survival for these patterns of involvement.  Four out of six patients with multifocal tumor died of disease; 5 of 7 with pneumonic involvement died of disease--all 5 of whom had mucinous BAC type.

Finally, they confirmed by multivariate analysis that stage (p=0.004) and histologic subtype (p=0.035) were independent prognostic factors for overall survival.  It would be nice to have this data presented as hazard ratios to assess the relative effect of each of these factors.

3.  Finally, Hata et al (J Thorac Oncol 2010;5:1197-1200) recently reported a study of EGFR and KRAS mutations in Japanese patients with mucinous BAC/adenocarcinoma with mucinous BAC subtype features (MBAC/AWBF).  They analyzed 20 cases of MBAC/AWBF for EGFR and KRAS mutations and compared them with 24 cases of N-MBAC/AWBF.  Briefly, they found in MBAC/AWBF there is a low incidence of EGFR mutations (3/20, 15%) while there is a frequent incidence of KRAS mutations (12/20, 70%).  Conversely, in N-MBAC/AWBF there is a higher incidence of EGFR mutations (14/24, 58%) but less frequent incidence of KRAS mutations (7/24, 29%).  Note that in contrast to the studies above, these authors did find some EGFR mutations in MBAC/AWBF tumors.  Moreover, the authors identified 3 patients with MBAC/AWBF with concomitant EGFR and KRAS mutations--thus showing that these mutations are not always necessarily mutually exclusive.  The reasons for these discrepancies may be methodological becasue of different mutation detection techniques or may be due to racial/ethnic differences.  Further work to examine differences across populations would definitely be interesting.  But, more importantly from a practical standpoint,  I think this is significant because it illustrates that we cannot simply use histology as a perfect triage for mutation testing.  It would be quite interesting to see if any of the 3 patients with MBAC/AWBF with EGFR mutations were treated with EGFR-TKIs and what the response was in comparison to other histologic types and subtypes.

Bottom line?  Pathologists should use the above information to try and differentiate mucinous versus non-mucinous subtypes in BAC/ACA with BAC features, especially in early stage tumors as this has prognostic and, possibly, therapeutic significance.  Also, although histological subtype can predict the likelihood of an EGFR mutation being present, it alone should not be used as a criterion for mutational testing, particularly for EGFR mutations.

Digital Case Challenge: Adenocarcinoma with Non-mucinous Bronchioloalveolar Features

It has been a long while since I've posted one of the cases I've worked on and now its time to clear off my desk (before our CAP inspection).

The patient is an 83-year-old white man, non-smoker, who presented 2 months prior to surgery with cough and shortness-of-breath and was found to have a left lower lobe infiltrate and pleural effusion.  After hospital admission and a course of antibiotics, the patient's symptoms initially improved.  However, he returned again about one month later with the same symptoms and persistent infiltrate.  Bronchoscopy revealed a mass-like lesion but cytologic studies were negative.  He underwent CT-guided biopsy of the infiltrate which showed adenocarcinoma.  He subsequently underwent lobectomy and that specimen showed three ill-defined mass-like areas of consolidation measuring, respectively, 7 cm, 5 cm and 3 cm each in greatest dimension.  All three areas were extensively sampled (1 block for every cm of the largest dimension of the tumor) and all showed a similar histological appearance.  Below is a typical area:

High-power view:

High-power view showing typical intranuclear inclusions:

Ancillary IHC stains were done to further characterize this tumor as mucinous vs. non-mucinous.

Mucin (above) and diastase-resistant PAS (below):

 
TTF-1 (above) and EGFR (below):

No areas showing definitive features of invasion were identified in any of the three gross areas of consolidation; however, given that none of these areas were submitted in their entirety, the most prudent diagnosis is adenocarcinoma with non-mucinous BAC features.  From the dimensions of these areas that I provided above, submitting these lesions in their entirety would be impractical.  Moreover, sections from grossly uninvolved areas between and adjacent to the gross areas of tumor also showed microscopic BAC.  One subcarinal lymph node (station 7), 1 hilar (station 10) and 3 lobar (station 12) LNs were negative for metastatic adenocarcinoma.

My next post will continue discussion of BAC in the context of this case, incorporating data from recently published papers that I hope you'll find helpful in the diagnosis of these tumors.

Grading system for lung adenocarcinoma still elusive

The August 2010 issue of American Journal of Surgical Pathology features an article from the Memorial Sloan Kettering Cancer Center group proposing a grading system for lung adenocarcinoma in stage 1 cancer.

Sica G, Yoshizawa A, Sima CS, et al.  A grading system of lung adenocarcinoma based on histologic pattern is predictive of disease recurrence in stage I tumors.  Am J Surg Pathol 2010;34:1155-1162.

The authors articulate the frustration pathologists experience in dealing with the histological heterogeneity of lung adenocarcinoma (ACa) since the vast majority are mixed subtype as well as the lack of an objective, clinically relevant grading system for lung ACa.  Recent literature has shown that mixed subtype tumors with solid or micropapillary components appear to have worse outcomes compared with those that do not, while tumors with a predominantly bronchioloalveolar (BAC) component appear to have a better prognosis.

An important part of this study is the idea of "comprehensive histologic subtyping" per the mothod outlined by Motoi et al (Am J Surg Pathol, 2008).  It is only by essentially submitting the entire tumor for histology that one can accurately assess the histologic heterogeneity of a tumor and semiquantitatively identify the various subtype components.  Another interesting feature of this paper is the use of a "concordance probability estimate" in their statistical analysis.  Although the term seems like more complex statistical jargon, this measure seems useful to me in that it provides an estimate of the ability of each grading system to predict the outcome for an individual case.

To identify patterns of dissemination of different histological subtypes, the authors retrospectively studied 73 stage IIA-IV primary lung ACa and corresponding metastatic tumors.  The majority of these tumors were composed of predominantly acinar subtype in 48%, solid subtype in 19%, and papillary in 19%.  While tumors at each of the metastatic sites also showed a mixture of patterns, the predominant subtype pattern was more likely to be found at the metastatic site.  Of note, even when the solid or micropapillary patterns were a small percentage of the primary tumor, these patterns are disproportionately more often found in the metastatic site.

Based on this work the authors devised a 3-tier grading system based on the mix of histological subtypes: grade 1, predominantly BAC pattern; grade 2, acinar and papillary, and grade 3, solid and micropapillary patterns.  The second part of this study was to test this grading system and a number of different scoring systems in 366 stage 1 ACa for the ability to predict disease-free survival (DFS).

In the stage 1 ACa group, predominantly acinar subtype was seen in 49%, papillary subtype in 26%, solid in 13%, BAC in 9% and micropapillary in 3%--a slightly different distribution (but perhaps expectedly so) compared to the high stage group.  But here is where this study, imho, jumps off the rails.  I refer the reader to Table 2 on page 1159 for more details but I'll try to summarize.

The authors show some value to reporting the most predominant grade which showed nice separation of DFS but only had a "concordance probability estimate" of 0.61--that is, in 2 randomly selected patients, this system would order them correctly with respect to DFS in 61% of cases.  The authors preferred scoring system based on the two most prominent grades only performed marginally better with a concordance probability estimate of 0.65.  In looking at the data, I would have preferred a scoring system of predominant grade + highest grade because this showed the best separation between the three tiers if you look at the 95% CI of the hazard ratios and yet still had a concordance probability estimate of 0.62.  The reality is that none of these systems actually perform well enough to warrent their clinical use.  The authors' own preferred system seems like it would be less reproducible than the others that were evaluated because it completely relies on semiquantitative estimates of proportions of patterns.  I think it could also underestimate the DFS for tumors which have small but significant proportions of solid and micropapillary patterns.

Anyhow, it is a start and much further work is needed before we get something that approaches, for example, the Nottingham scoring system for breast cancer.

 

 

Uncommon Lung Adenocarcinoma Variants: a mini-review

There are five common types of adenocarcinoma (actually I would say four since "mixed" doesn't seem to me a specific 'type") recognized in the WHO classification of lung cancer.  But this classification also includes five rare but distinctive variants: fetal adenocarcinoma, mucin-producing adencarcinomas (mucinous "colloid" adenocarcinoma, mucinous cystadenocarcinoma, and signet ring adenocarcinoma), and clear cell adenocarcinoma.  

While rare to exceedingly rare as pure tumors, the variant patterns are important to be aware of because they occur much more commonly as a component of mixed type adenocarcinomas, are associated with particular clinicopathologic features, and often require the exclusion of a different primary site.  Another challenging variant is the nonmucinous lung adenocarcinoma which resembles colorectal adenocarcinoma but I'll review this variant in another post.  Hope you all find this of use.

Fetal adenocarcinoma

• Unencapsulated but well-circumscribed composed of closely packed branching tubules with little intervening stroma resembling fetal lung seen between 10 and 16 weeks' development (pseudoglandular stage).
• Cribriform arrangements can be prominent and cells arranged in cords and ribbons with peripheral palisading also described.
• The tubules are lined by "endometrioid" nonciliated pseudostratified columnar cells with frequent subnuclear or supranuclear vacuoles.
• Structures resembling squamous morules as in endometrioid adenocarcinoma are often present and the nuclei in these foci often appear optically clear (nuclear pseudoinclusions) due to biotin accumulation.
• Frequent mitoses.  Variable necrosis--focal to extensive.
• Low-grade and high-grade variants are recognized which differ significantly in clinical and histopathologic parameters:
• • Low-grade: mean age 34 years, about equal M:F, usually present at early stage, associated with a good prognosis; orderly arrangement of glands, focal necrosis (if present at all), small fairly uniform nuclei with inconspicuous nucleoli, morules common; slight to moderate loose fibromyxoid stroma, neuroendocrine differentiation almost always found, occasional AFP-positive cells, p53 protein overexpression uncommon, nuclear and cytoplasmic β-catenin expression
  • High-grade: mean age 64 years, male predominance, usually advanced stage at presentation, associated with poor prognosis (42% [email protected] mos.); disorderly arrangement of glands, extensive areas of necrosis common, large pleomorphic nuclei with prominent nucleoli, morules absent, abundant desmoplastic stroma, always AFP-positive cells, p53 overexpression common, membranous β-catenin expression

Mucin-producing adenocarcinomas

Morphologically similar to non-pulmonary mucinous carcinomas from GI tract, pancreas, ovary, and breast.

Mucinous (colloid) adenocarcinoma

• Rare as a subtype but mixed tumors frequently show mucinous morphology
• Appears same as in other organs in which it is more frequently encountered: dissecting mucin pools containing islands and strips of mucinous epithelium with malignant cytologic features
• In the lung, mucinous columnar cells can focally line alveoli in a lepidic pattern.
• The neoplastic goblet cells express enteric markers (CDX2, MUC2 and CK20) with inconsistent, focal and weak CK7 and TTF-1 expression--thus, clinical correlation is needed to diagnose this as a pure lung primary.
• • Primary lung mucinous BAC does not show mucin pools invading stroma, is primarily composed of neoplastic mucinous cells lining alveolar walls, and does not show expression of CDX2 or MUC2.
• This neoplasm should be considered a low-grade carcinoma with more favorable survival rates compared to mucinous BAC or conventional mixed adenocarcinoma.

Mucinous cystadenocarcinoma

• Like the ovarian counterparts, this groups of tumors shows a histologic spectrum encompassing benign (mucinous cystadenoma), borderline (mucinous cystic tumor of borderline malignancy) and malignant (mucinous cystadenocarcinoma).
• The cytological and architectural criteria for differentiating these tumors are also similar to those in the ovary, except that invasion of surrounding lung is diagnosed as a mixed subtype of adenocarcinoma (for reasons I'm not quite clear but there it is).
• The mucinous epithelium in all of these cystic lesions differ from the mucinous adenocarcinoma type in that these express CK7 but inconsistently express CK20 and TTF-1.  These are quite rare and have been studied for MUC2 or CDX2.

Signet ring adenocarcinomas

• Rare as a pure subtype and uncommon (around 2%) as a component of mixed adenocarcinomas.
• Younger average age when predominant as a component compared to average age of lung cancer patients in general
• Unlike the other subtypes, this variant is defined by cytology--the classic signet-ring morphology.
• Intracytoplasmic material stains with PAS diastase, mucicarmine, and Alcian blue @ pH 2.7--indicating both neutral and acid mucins
• Over 95% of tumors express CK7 and over 80% express TTF-1 but are negative for CK20; also positive for CEA, MUC1 and MUC5AC--a staining profile that helps distinguish this as a primary lung tumor versus metastasis from breast, gastric and colon primaries.
• This is the most aggressive mucinous-type lung adenocarcinoma.
• Tumors with at least 50% signet-ring component have a poorer 5-year survival rate compared to the typical adenocarcinoma prognosis.

Clear cell adenocarcinoma

• Extremely rare as a pure subtype--but over a third of mixed adenocarcinomas show at least some focal clear cell change.
• Tumor cells form sheets with at least focal tubal formation (the latter required for diagnosis) and may form papillae.
• Intracytoplasmic material is PAS-positive, diastase-sensitive--indicative of glycogen.
• Pure tumors have not been well-studied by IHC--one reported tumor was CK7+/CK20-/TTF-1+.
• Distinguishing primary lung clear cell adenocarcinoma from a renal metastasis requires
• • clinical and radiologic correlation
  • identifying a mixed growth pattern and intracytoplasmic mucin
  • finding IHC markers specific for RCC
     

Screening for EGFR and KRAS mutations by clinicopathologic features

Dr. Sonia Dacic and the lung pathology group at University of Pittsburgh Medical Center recently published in Modern Pathology an article (full text here), "Clinicopathologic predictors of EGFR/KRAS mutational status in primary lung adenocarcinomas."  The authors state that the aim of the study was "to determine whether clinicopathological characteristics and morphology of lung adenocarcinomas might be used as predictors of tumor mutational status, which then may be implemented as the selection criteria for molecular profiling of lung adenocarcinomas in clinical practice."  Implicit in this statement are the assumptions that molecular testing of lung adenocarcinoma is expensive and that screening cases for molecular testing by morphological criteria would be cost-effective.

This is a single institution study of 345 previously untreated, surgically resected lung adenocarcinoma cases from UPMC.  One important methodological issue is the uniform histological assessment of every tumor using 2004 WHO classification criteria and assessment of percentages of various histological subtypes of adenocarcinomas.  All tumors underwent KRAS and EGFR mutational analysis and assessment of EGFR amplification by FISH.  One potential weakness of this study with respect to its possible general application is the marked over-representation of stage I tumors (201 out of 345) and slight over-representation of women (57%) and never smokers (12%) compared to the general population--indicating a possible referral bias.  All three groups would be expected to enrich the study population for EGFR mutations/amplification.  However, the frequencies of EGFR and KRAS mutations are similar to other studies (about 10% EGFR mutated and 30% KRAS mutated tumors).  One weakness of this study (which the authors point out as well) is the lack of survival analysis--however, given the overabundance of stage I tumors, I'm not sure how generally applicable that data would be unless they focused on finding stage I subgroups with different survival outcomes.  Their data also confirmed previously reported associations between EGFR mutations and female sex and never smoker history.  

• The absence of solid growth pattern was a significant predictor of EGFR mutation, while mucinous growth pattern was a significant predictor of KRAS mutation.
• A prominent lymphocytic host response was significantly associated with KRAS+ and EGFR-/KRAS- tumors than EGFR+ tumors.
• There was no correlation between morphology and EGFR FISH positivity.

The authors' findings are consistent with previous studies of U.S. patients but the association found between lymphocytic host response and EGFR mutation status is a novel and interesting finding.  The issues of TILs and peritumoral lymphocytic host response are controversial "hot topics" in solid tumor research and warrants further investigation in lung cancer research.

There is wide variation in testing for mutations in lung cancer ranging from institutions that test all lung adenocarcinomas to those which test upon request.  I agree with the authors about the need for an algorithmic approach to testing, although I disagree about a "universal" one.  Currently, one can propose several different algorithms that would each be "rational" and "evidence-based" but I don't think one would prove superior to the other, especially when deployed in a wide variety of settings.  With mutation-specific MoAbs coming online for IHC, this picture should be even more textured.  Back to the paper, none of the clinicopathologic criteria can be used to select lung adenocarcinoma cases for targeted testing due to the morphologic heterogeniety of lung adenocarcinoma itself and the large overlap between tumors with and without EGFR and KRAS mutations (just the two most common mutations!).