The Daily Sign-Out

BRAF mutations in colorectal cancer: mini-review

There has been a recent flurry of papers and reports from ASCO-GI 2013 pushing more molecular testing in colorectal cancer (CRC) and its clinical significance with regard to prognostic and predictive factors, especially with MMR/MSI.

One area that caught my interest was BRAF mutations in colorectal cancer. Given the justifiable excitement around BRAF-mutated malignant melanoma responses with vemurafenib, I was curious about BRAF mutation in CRC. Here's my notes--

• 5% to 10% of CRCs have the BRAF mutation and the predominant mutation is similar to that seen in a large minority of melanomas, viz, the V600E mutation.
• Activating mutations in BRAF lead to constitutive activation of downstream signaling through the MAPK/MEK/ERK pathway.
• Recognition of this led to reflexive testing for BRAF if a CRC tumor was found to be KRAS-wildtype, since BRAF-mutant tumors would also be resistant to therapy with cetuximab similar to KRAS-mutant tumors.
• BRAF mutation appears to occur early in CRC progression and is associated with CpG island methylation.
• It leads to serrated adenoma-type polyps that have defective mismatch repair leading to a tumor that displays microsatellite instability.
• Important clinicopathologic associations: female gender, older age, right-sided location, high histologic grade, MSI-high--but not HNPCC.
• Advanced stage BRAF-mutated tumors have a poor prognosis: in a study of 524 patients with metastatic CRC (mCRC) by Tran et al. in Cancer (2011), OS for patients with BRAF-mutant tumors was 10.4 months versus 34.7 months in patients with BRAF-wild type tumors.
• Unlike the 81% response rate with vemurafinib in BRAF-mutated melanomas, the response rate in patients with mCRC is only about 5%.
•         ?more heterogenous distribution of BRAF mutation in CRC
•         similar mutations do not equal similar tumor biology (and thus) response to same targeted therapy
• In CRC (and in general?), mutations need to be viewed in context of other signaling pathways--
• Data from CRC cell lines and clinical tissue specimens show that BRAF mutation alone is insufficient for vemurafinib sensitivity: CRC can escape through activation of the PTEN/PI3K/AKT pathway and feedback activation of EGFR or other RTKs. This suggests multiple pathway inhibition as a possible therapeutic strategy in BRAF-mutant CRC.

Still lots of questions with this distinct subset of CRC--stay tuned.

 

New proposal for histological grading in colorectal carcinoma

I find it surprising that histological grading for two of the most common adult malignancies--colon and lung--lacks any kind of consensus criteria for grading elements let alone clinical validation as a prognostic marker.  I have previously blogged on proposals for grading for lung adenocarcinoma but the February 2012 issue of American Journal of Surgical Pathology has an intriguing proposal for criteria for grading of colorectal cancer by Hideki Ueno et al. (abstract).

I am most familiar with Dr. Ueno's previous work on tumor budding in colon cancer (you should be too!) and this work builds on and expands on this work.  In contrast to tumor budding, defined as invasive single cells and/or clusters with <5 cells, this work describes and defines the significance of "poorly differentiated clusters" for grading.  Poorly differentiated clusters are defined by these authors as "cancer clusters in the stroma composed of >5 cancer cells and lacking a gland-like structure."  These clusters are identified at low power and then counted per 20X (1-mm diameter) field.  The color illustrations included in the text are particularly well-selected and beautifully reproduced.  Grading was also assessed independently by assessing quantitatively the area of the tumor involved by poorly differentiated clusters and by tumor budding.

Although this is a single institution study, it included 500 consecutive patients with stage 2 or stage 3 CRC who underwent curative resection and had follow-up on 97% (!) of these patients (483 patients) for a median of 68 months for the 378 surviving patients.

Three things stand out from the results.  First, there was excellent separation in 5-Year DFS using quantity of poorly differentiated clusters as the criterion for grading: grade 1--96%, grade 2--85%, grade 3--59%.  Second, tumor grading based on poorly differentiated clusters, T and N stages, and venous invasion were independent prognostic parameters related to survival on mutlivariate analysis.  FInally, the authors measured intra- and inter-observer variability in tumorg grading based on poorly differentiated clusters.

This is an interesting and status quo-challenging article that should provoke some good discussion amongst GI specialist and general pathologists.

Review of microsatellite instability (MSI) in colorectal cancer

Clinical Cancer Review just published an "OnlineFirst" article on February 2, 2012 (link to abstract) that reviews microsatellite instability (MSI) in colorectal cancer.  There have been several recent reviews on this topic in various journals, including Archives of Pathology and Laboratory Medicine in October 2011.  The review by Drs Geiersbach and Samowitz in Archives is excellent (and recommended too) but has a decidedly technical, lab-oriented focus. I recommend this one to pathologists looking for a more clinically-oriented review that especially addresses current and future studies looking at how the molecular heterogeneity of "MSI" tumors may have different chemosensitivity responses.  It is very readable and certainly is the most current.  If you're looking for an article that makes you look good in tumor board, this is it!

A couple of highlights:

• MSI as prognostic marker in CRC.  Observational studies, retrospective data from randomized clinical trials and meta-analyses have consistently shown that tumors that show MSI or deficient mismatch repair (MMR) are independently associated with improved survival and reduced recurrence rates compared with individuals with MSS tumors.
• ECOG 5202 is a ongoing trial of stage II CRC patients stratifying them into low-risk versus high-risk based on MSI and allelic loss of 18q.  Low-risk patients (MSI and intact 18q) are assigned to an observational arm post-op while high-risk patients (MSS and allelic loss of 18q) are assigned to standard post-op chemo for stage III patients (FOLFOX).  Unfortunately, this study will not address the use of MSI as a predictive marker for response to 5-FU therapy.
• MSI as predictive marker in CRC.  Mutliple studies, including RCTs, retrospective case series, in vitro cell line data, and a meta-analysis, have consistently shown that MSI is a negative predictive marker for response to 5-FU.  It has been recently recommended that patients with stage II colon cancer showing MSI not receive 5-FU as adjuvant therapy given their favorable prognosis and lack of benefit from 5-FU.  Incidentally, in discussing whether to routinely test for MSI in stage II and II patients with the oncologists, it was evident that there is a lot of "catch-up" and education that needs to be done here. 
• Currently, there are only limited data in MSI tumors from patients treated with oxaliplatin combined with 5-FU and predictive information is lacking.  This is an important confounding problem interpreting the literature since standard first-line treatment for CRC is 5-FU and oxaliplatin.  It appears, however, from in vitro studies that oxaliplatin sensitivity is independent of the MMR system.
• Since KRAS testing is becoming more routine for CRC, especially in high stage III/stage IV cancers, it is important also to note that sporadic MSI CRCs (with epigenetic inactivation of hMLH1) show frequent (~50%) co-occurrence of BRAFV600E mutations (compared to an overall BRAF mutation frequency of about 10% among all CRCs).  Note: The presence of a BRAF mutation indicates a sporadic MSI CRC and essentially excludes a diagnosis of Lynch syndrome.
• There's a lot of interesting stuff on possible additional targets for therapy you should check out.

Examination of colon specimens resected for polyposis

One of my colleagues received a 40-cm left colectomy specimen from a 49-year-old woman that I diagnosed with a grade 1 T3N0 cecal adenocarcinoma in August of 2011.  MMR testing by IHC at that time showed proficient (or intact) MMR proteins.  The specimen contained around 20 or so separate and discrete polyps with a range of sizes (0.4 to 1.5 cm) and configurations (pedunculated to sessile)--but none which appeared grossly canacerous.

We consulted our trusted tomes and PubMed but were unable to find any published protocols for what constitutes even "adequate" sampling for colectomy specimens resected for polyposis.  Is anyone out there aware of such a protocol?

My colleague (wisely) decided to sample all the sessile and/or >1 cm polyps.  As it turned out, a T1 adenocarcinoma was identified in one such polyp and a Tis lesion in another.  Lymph nodes were negative but, I would add, the surgery was performed laparoscopically and the mesenteric cuff was (ahem) abbreviated.

Any thoughts?

Recent article collection on colorectal cancer

Nature Reviews Clinical Oncology and Nature Reviews Gastroenterology and Hepatology have put together a superb collection of state-of-the-art reviews on various aspects of colorectal cancer that is currently free to access and download.

This collection of articles published in the past 18 months from these journals comprises a selection of 9 Reviews, 3 Perspectives, 17 News & Views, and 12 Research Highlights that discuss advances in the understanding of the screening, diagnosis, prevention and treatment of this disease, as well as highlighting the challenges and future directions in this field.

There is a tonne of great content here that, if anything else, gives you a one-stop shopping reference and the material is timely and relevant.

Nice reading for a lovely fall weekend!  Don't forget to set your clocks back Saturday night.

Prognostic factors in T1 colorectal adenocarcinoma

A frequently encountered specimen is the adenocarcinoma with submucosal invasion arising in a dysplastic adenomatous polyp or sessile lesion that has been resected endoscopically.  While much effort is directed at determining margin adequacy and depth of invasion, less attention has been given to other parameters that may be associated with risk of lymph node (LN) metastasis. Measuring the depth of invasion is frequnetly problematic given the morcellated nature of most specimens.  Generally, if the lesion is felt to be adequately excised, a formal colectomy may not necessarily be needed since the risk of LN metastasis in a T1 tumor is felt to be too low to warrent the morbidity of a colectomy.

A recent article in the August 2010 Modern Pathology sought to detect patients at high risk for LN metastasis after endoscopic mucosal resection.

Tateishi Y, Nakamishi Y, Taniguchi H et al.  Pathological prognostic factor spredicting lymph node metastasis in submucosal invasive (T1)colorectal adenocarcinoma.  Mod Pathol 2010;23:1068-1072.

This is a single-institution study that examined 322 consecutive patients treated by colectomy (complete tumor excision plus lymphadenectomy) for T1 colorectal adenocarcinoma.  The entire lesion was examined microscopically in all cases and criteria evaluated for the study included submucosal invasive depth, tumor size, lymphatic invasion, venous invasion, histologic grade, tumor budding at the submucosal invasion front, and status of muscularis mucosae.

The authors found LN metastases in 14.3% of patients (46/322)--which was a surprising and sobering finding in itself to me.  By univariate analysis, tumor budding, histologic grade, lymphatic invasion, venous invasion, submucosal invasion depth > 1 mm, and completely disrupted (type B) muscularis mucosae were associated with LN metastasis.  By multivariate analysis, however, only tumor budding, high grade tumor differentiation, and lymphatic invasion were associated with LN metastasis.  Moreover, of the 46 patients with LN metastasis, 40 (87%) had at least 1 out of 3 factors by multivariate analysis associated with LN metastasis; the remaining 6 all showed type B muscularis mucosae status.  Using these four criteria, 285 out of 322 patients were positive for at least one criteria and would have undergone colectomy after submucosal resection--for 100% sensitivity but only 13.4% specificity.

Certainly, the decision whether colectomy is the most appropriate definitive treatment following endoscopic resection must be individualized.  But it seems in my experience that this is a gray zone for surgeons and oncologists and these criteria, while needing independent and prospective validation, are worthy of further study and consideration of being adopted for routine use now.  The evaluation of muscularis mucosae status is not familiar in the U.S. and the reader is referred to the original article by Tominga et al in Dis Colon Rectum (2005) for more detail.

The practical points here are 1) that these parameters can be readily assessed in routine H&E sections and 2) using four histologic risk factors--tumor budding, lymphatic invasion, high-grade histologic tumor differentiation (moderately- to poorly-differentiated), and type B muscularis mucosae status--the authors were able to select all patients who were shown to have LN metastasis. 

Colonoscopy recommended at earlier age for black patients

from ASCO "Cancer in the News"

"HealthPartners to encourage black patients to begin colonoscopies at 45.HealthPartners Medical Group announced a new program to encourage black patients to start getting colonoscopies at age 45 "because blacks are at higher risk than whites of dying from colon cancer...said" Dr. Brian Rank, a cancer specialist and medical director of HealthPartners. Rank noted that "nationally, colorectal cancer deaths are 48 percent higher among African-Americans than among Caucasians." The program makes HealthPartners "one of the first medical organizations in the nation to use racial information about patients to customize their medical care."

This is a significant move recognizing differences in cancer biology (and thus outcomes) that are related to racial/ethnic differences observed in the American population. Although this is a complex and sensitive area, this is a welcome intervention that attempts to integrate available data and practice. Certainly more research into racial differences in cancer biology is needed in general. Differences in lung cancer between Asian and American populations has yielded interesting biological differences that are being translated to practice with respect to TKIs.  
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Nodal Staging Score: A Tool to Assess Adequate Staging of Node-Negative Colon Cancer -- Gönen et al. 27 (36): 6166 -- Journal of Clinical Oncology

Gonen, Schrag and Weiser recently report a study of colorectal cancer patients from the 1994-2005 SEER database to quantify the likelihood that a node-negative patient is, in fact, node-negative.  This is an interesting alternative method of assessing adequate staging of CRC in contrast to the usual "one-size-fits-all" minimum lymph node criteria (namely, 12). 

They have developed a "nodal staging score" (NSS) that expresses the probability of a patient being "true negative" and find that this score depends on the T stage.  Overall, the probability of missing a positive node that is actually present is 29.7% if only 5 nodes are examined; 20.0% if eight are examined; 13.6% if 12 nodes are examined.  However, for a NSS of 90% (that is, a 90% likelihood that the patient is truly node-negative), a single node is sufficient for T1 tumors, 4 nodes for T2 tumors, 13 nodes for T3, and 21 nodes for T4. 

The authors provide graphical and tabular tools are provided to facilitate calculation of NSS and treatment decision making for daily clinical practice.

I question whether a 90% likelihood is good enough--I am not comfortable with that at all, especially at the T2 stage.  Four nodes just is not adequate and the implications are fairly significant.  It would be interesting to re-evaluate the data for NSS at 95% or 97.5%.  It seems, interestingly enough, that--at a major critical clinical point, the T3 tumor, the minimum number of nodes (at least for a NSS of 90%) is 13--very close to the current 12-lymph node standard.  Biologically, this makes perfect sense in that, intuitively, a node-positive T1 tumor ought to be very uncommon and the burden of proof would definitely be on the pathologist to demonstrate that a patient with a T4 tumor is indeed node-negative (gotta show me more than 12 nodes!).

Very thought-provoking study.

Nodal Staging Score: A Tool to Assess Adequate Staging of Node-Negative Colon Cancer -- Gönen et al. 27 (36): 6166 -- Journal of Clinical Oncology

Leave well enough alone? The role of resection in asymptomatic metastatic CRC

The standard of care for treatment of mCRC has been surgical resection followed by adjuvant chemotherapy.  In patients presenting with symptomatic mCRC, palliative surgery is performed for bleeding, obstruction, or perforation, while in patients presenting with non-emergent symptoms and limited disease, surgery may be undertaken with a curative intent.  The role and value of surgery in patients with unresectable stage 4 colon cancer and a synchronous asymptomatic primary tumor is being currently investigated by the National Surgical Adjuvant Breast and Bowel Project in a prospective phase II study (NSABP C-10).  Current recommendations for treatment of mCRC are:

1. Patients with evidence of significant obstruction, perforation, or uncontrolled bleeding should undergo resection of the symptomatic lesion.
2. Patients who are unfit for surgery, or who decline surgery, should undergo endoscopic management with stents or ablation to palliate symptoms.
3. Patients with potentially resectable metastases should undergo resections of both the primary tumor and the metastases (typically, sequentially).
   1. Chemotherapy may be administered preoperatively to assess the natural history of the underlying malignancy.
   2. If disease controlled is obtained with chemotherapy, resection of primary and secondary lesions should be considered.
4. In patients who have diffuse, metastatic CRC with unresectable metastases, modern polychemotherapy with targeted agents will offer disease control without the mortality and morbidity of surgery directed at the primary lesion.

The hypothesis of this study is that, given the dramatic improvement in response rates with current regimens incorporating oxaliplatin and irinotecan with biologics such as bevacizumab and cetuximab, systemic chemotherapy without resection of the primary tumor is a reasonable alternative to the standard approach in these patients.  This approach takes into account the morbidity and mortality associated with colectomy in these patients compared to the potential survival benefit in an incurable disease where <10% of patients survive 5 years. 

Patients  will be treated with 5-fluorouracil, leucovorin, and oxaliplatin (mFOLFOX6) plus bevacizumab. The goal is to determine if this approach leads to an increase in “major morbidity” defined as any event related to the intact primary tumor necessitating surgery or resulting in patient death. The results of this study should be very interesting and could represent a real change in thinking about how we treat primary tumors. Oncologist. 2009;14(10):963-969.

More recommendations for lymph node adequacy in CRC

The Dutch National Working Group on Gastrointestinal Cancers has recently released colorectal cancer guidelines which includes a recommendation of a minimum of 10 lymph nodes to establish a negative lymph node status.  At the same time, the group states that "determining the lymph node status of a patient requires evaluation as many lymph nodes as possible using conventional techniques." (emphasis mine

The discussion of this recommendation states that "no definitive criteria were found in the literature regarding the minimum number of examined lymph nodes.  There is no evidence to support 12 lymph nodes, as recommended by TNM." (emphasis mine)

Furthermore, they specifically do not recommend using immunohistochemistry to detect metastases or pre-treatment of mesenteric fat with GEWF-type solutions.  While using the former to detect micrometastases is not common practice, as least in the U.S., the latter is not only fairly common, if not routine in many places (mine included!).  Also, the recent literature also supports the use of these solutions to increase lymph node retrieval, although the utility of the raw node count has been questioned with the data regarding the percentage or proportion of positive:negative nodes (whole other discussion!).