Mucinous differentiation in prostatic adenocarcinoma.

Morphologic and histochemical analysis was performed on 33 carcinomas with mucin-secreting areas that were identified among 100 carcinomas from radical prostatectomy specimens. The most common mucin-secreting pattern was Gleason grade 3, which usually showed distinctive luminal distention. The "colloid carcinoma" pattern with mucinous lakes was the only histologic pattern that was unique to mucinous areas. Its frequent association with cribriform Gleason grade 4 carcinoma suggests that it is a variant of grade 4 cancer, whose deviant appearance is a consequence of mucus hypersecretion. Collagenous stromal micronodules, found in 13 cases, are a previously undescribed and distinctive pattern thought to be a stromal reaction to contact with acidic extraluminal mucin. In grade 3 carcinoma, glands that secreted into the stroma rather than the gland lumen accounted for the stromal mucin, which appeared to lead to micronodule formation. In the grade 4 "colloid cancer" pattern, collagenous micronodules sometimes completely obliterated mucinous lakes, isolating residual cribriform glands in a "pseudo-grade 3" pattern. Lectin histochemical staining showed similar sialated and/or sulfated acidic mucin in all cases. Immunohistochemical staining showed downregulation of several differentiation antigens accompanying the alteration to mucinous differentiation.