Morphometric analysis of the "mucocellular layer" overlying colorectal cancer and normal mucosa: relevance to exfoliation and stool screening.

Characterization of shed cell elements entrapped within the colorectal surface mucus would be valuable to the study of exfoliation and candidate stool screening markers. Yet, surprisingly little is known about the cellular composition of this "mucocellular layer" (MCL). Our aim was to describe and compare the histomorphometry of the MCL that overlies colorectal cancer (CRC) and normal mucosa. From tissue archives, 20 resected CRC specimens yielding perpendicular cuts of both tumor surface and adjacent normal mucosa were consecutively selected. MCL thickness and cell number were determined in triplicate using an ocular micrometer. Cellular elements within the MCL were characterized on paraffin sections by immunohistochemistry. Mean cell density was much greater in the MCL over CRC (2,639 +/- 2,178 per mm2) than over normal mucosa (184 +/- 395 per mm2), p < .001. Robust-appearing colonocytes and inflammatory cells predominated in the hypercellular MCL of CRC; the former retained expression of tumor-associated antigens. In contrast, the sparsely scattered cells within the normal MCL were typically apoptotic and of indeterminate lineage. Based on direct observations from this first descriptive study of the colorectal MCL, luminal shedding appears to be much greater from CRC than from normal mucosa.