MUC2 expression in primary mucinous and nonmucinous adenocarcinoma of the prostate: An analysis of 50 cases on radical prostatectomy

The expression of mucin (MUC2) in prostate cancer has not been well studied previously and may be of prognostic and pathobiologic significance. It is, however, well known that MUC2 expression in mucinous pancreatic and breast cancer represents an indolent pathway since these tumors have a significantly better outcome than their conventional counterparts. Twenty-five cases each of Gleason pattern 3 and 4 mucinous adenocarcinoma of the prostate defined by greater than 25% mucinous component and nonmucinous adenocarcinoma of the prostate were obtained from the surgical pathology files of the Johns Hopkins Hospital and Emory University Hospital. Immunohistochemical stains were performed for MUC2 on all 50 cases. Mean patient age was 60 years (range 44-72 years). MUC2 was expressed in all 25 cases (100%) of mucinous adenocarcinoma of the prostate, irrespective of the Gleason pattern. The nonmucinous component of these cases was negative for MUC2. In contrast, MUC2 expression was significantly lower in nonmucinous adenocarcinoma of the prostate, detected in only 6/25 cases as a focal finding, while 19/25 (76%) of nonmucinous adenocarcinoma of the prostate were completely negative for MUC2 (P<0.01). In six cases that showed focal positivity, MUC2 was expressed in areas with Gleason pattern 3 cancer with extensive mucinous fibroplasia (one case) and prominent intraluminal mucin (five cases). Other areas of these tumors were negative for MUC2. Mucinous adenocarcinoma of the prostate shows diffuse expression of MUC2, a known tumor suppressor, which is not present in either normal prostate or the majority of conventional adenocarcinomas of this organ. This indicates that mucinous adenocarcinoma of the prostate is indeed of the 'colloid type' akin to those in other exocrine organs. It is highly conceivable that this de novo expression of MUC2 has a role, not only in the mucinous differentiation of these tumors and their colloid pattern, but also in their relatively indolent behavior that has been recently elucidated.