Contact between abluminal microvilli and collagen fibrils in metastatic adenocarcinoma and mesothelioma.

It can be difficult to differentiate between epithelial and mixed type mesothelioma and metastatic adenocarcinoma. To distinguish between the two, it has recently been suggested that the presence of abluminal microvilli making contact with collagen fibrils through discontinuities in the basal lamina was characteristic of mesothelioma but not of metastatic adenocarcinoma. This study presents three patients out of 39 who had adenocarcinoma metastatic to the pleural and abdominal cavities, in which direct contact was observed between abluminal microvilli and collagen fibrils. All 39 examples of mesothelioma which were also examined demonstrated this feature. This phenomenon should therefore not be used as a discriminator between mesothelioma and metastatic adenocarcinoma. An additional patient with metastatic adenocarcinoma in an axillary lymph node demonstrates that this phenomenon is not limited to the pleural or abdominal cavities.