So many great articles at the end of the year, it's going to take me 'til Easter to catch up!
The December 2010 issue of American Journal of Surgical Pathology has a fascinating article from Dishop and (multiple) colleagues reporting 10 morphologically distinct tumors from multiple American institutions. The patients' ages ranged from 0 days to 3 months and imaging in each case revealed a well-circumscribed lobar-based mass. Lobectomy or wedge resection was performed in each case.
Each tumor was a well-circumscibed intraparenchymal mass with a solid-to-spongelike surface that appeared to be at least partially surrounded by a fibrous capsule. The microscopic appearance was characterized by an abrupt transition from normal saccular-stage lung to more immature-appearing, variably-sized and -shaped spaces separated by cellular septa with variable width. The lining epithelium is composed of regularly distributed non-ciliated flattened to cuboidal cells. The interstitium is composed of a monotonous population of uniformly distributed round-to-ovoid mesenchymal cells. None of the cases showed any of the malignant features associated with pleuropulmonary blastoma (PPB).
The interstitial cells showed diffuse positivity for vimentin and variable staining for smooth muscle actin and desmin; the epithelial cells were positive for cytokeratin (clone not specified) and EMA but TTF-1 positivity was reported in only 1 case.
Fetal lung interstitial tumor (FLIT) is the term proposed by the authors to describe a lobar-based tumor well-demarcated from surrounding normal lung that presents either prenatally or within the first 3 months of age, is composed of variably sized cysts composed of histologically benign epithelium and interstitial cells, and shows apparently benign clinical behavior.
The authors discuss the possible relationship between "FLIT," type I (cystic) PPB, and congenital peribronchial myofibroblastic tumor (CPMT) and posit a growth disorder in pulmonary interstitial cells as a common histogenesis for these rare, curious tumors.
I realize that this is a highly subspecialized report that is probably of little general interest. BUT check this: tumors such as these point to the complex interactions between endodermally-derived epithelium and mesodermally-derived mesenchyme during lung development--an interaction which plays itself out again in more common lung diseases, like ILDs and lung cancer!