Cancer Prevention Research Identification of Mucin Depleted Foci in the Human Colon

Aberrant crypt foci (ACF) originally described in rodents treated with colon-specific carcinogens have been identified also in humans at high risk of colon cancer (CRC) and are extensively used as cancer biomarkers. However, studies documenting the heterogeneity of ACF have questioned their precancerous nature. Recently, we described dysplastic foci depleted of mucins (MDF) in the colon of rats treated with colon-specific carcinogens. Like colon tumors, MDFs show activation of Wnt signaling driven by mutations in the β-catenin gene and Apc, a key gene in colorectal carcinogenesis. Because MDFs have been identified thus far only in rodents, we wanted to search for similar lesions in humans. Familial adenomatous polyposis (FAP) subjects, carrying germ-line mutations in the APC gene, are at high risk of CRC. Therefore, we first searched for MDF-like lesions in unsectioned colon samples from FAP patients and then in patients with sporadic CRC. MDFs were present in the colon of FAP patients (average of 0.0577 lesions/cm) and at a much lower density in CRC patients (average of 0.0006 lesions/cm). ACFs were also observed in all patients. Histologic preparations of all the MDFs identified in FAP and CRC consisted of microadenomas at variable grades of dysplasia. The occurrence of MDF-like lesions in high-risk patients provides evidence that these lesions have a counterpart in human pathology and, as observed in rodents, may represent the very early stages of CRC. Foci of aberrant crypts (ACF), microscopically visible in the unsectioned colon of carcinogen-treated mice, were originally described by Ranjana Bird in 1987 as being related to the early steps of colon carcinogenesis (1). The results of many studies characterizing ACF (2–4) and the demonstration that ACF-like lesions are also present in humans (5, 6) have reinforced the hypothesis that ACFs are precursors of colon cancer (CRC) and have led to their widespread use as biomarkers of colon carcinogenesis (7, 8). However, reports documenting the heterogeneity of ACF and their relationship with cancer not always straightforward (9–12) opened a debate on the validity of ACF as surrogate end points, stressing the need for additional biomarkers more robustly correlated with cancer (12–15). Recently, mucin depleted foci (MDF), formed by dysplastic crypts with scant or absent mucin production, were identified by our group in the colon of rodents treatedwith azoxymethane or 1,2-dimethylhydrazine (16), which induces CRC through histologic and molecular alterations similar to human carcinogenesis (17). Like ACFs, MDFs are easily identified in unsectioned colon. Moreover, studies carried out by us and others indicate thatMDFs are correlatedwith carcinogenesis and can thus serve as cancer biomarkers in chemoprevention studies (18–21). We documented that MDFs share pathologic and molecular alterations with more advanced lesions, such asWnt pathway activation, caused in part by mutations in the β-catenin gene (19). Moreover, the fact that MDFs carry mutations in the Apc gene at a frequency similar to tumors (22) reinforces the hypothesis that MDFs are precursors of CRC in rodents. MDFs have been identified thus far only in rodents treated with azoxymethane/1,2-dimethylhydrazine; therefore, we thought it important to show that lesions similar to MDF are also present in humans. Familial adenomatous polyposis (FAP) subjects, carrying germ-line mutations in the APC gene, are at high risk of developing CRC (23). Therefore, we began by searching for MDFlike lesions in FAP patients. We also studied patients with sporadic CRC because they are also at risk of developing a second CRC (24). In the same samples in which we searched for MDF-like lesions, we also studied ACF. Histologic analysis of the various lesions identified was then done. Materials and Methods