Lymph node metastases of prostatic adenocarcinoma in the mesorectum in patients with adenocarcinoma or villous tumor of the rectum with collision phenomenon in a single lymph node: report of five cases.

Purpose: Lymph node involvement is the most important prognostic factor when staging patients with rectal cancer. Cancer originating from sites other than rectum rarely may metastasize to the mesorectum. We report five patients with metastatic prostatic carcinoma to mesorectal lymph nodes, with the "collision phenomenon" in one lymph node. The diagnosis of prostate cancer was clinically unsuspected in two cases.

Methods: We examined three cases of primary adenocarcinoma and two villous tumors with high-grade dysplasia (patient age range, 52-74 (mean, 63) years) of the middle or lower third of the rectum. All patients underwent low anterior rectal resection with total mesorectal excision and colorectal or coloanal anastomosis. We used a manual technique for lymph node detection after overnight fixation in 10 percent formalin. All lymph nodes identified (range, 15-32; mean, 21 nodes per patient) were examined histologically.

Results: Of 106 lymph nodes examined, 20 contained metastases: 9 from rectal adenocarcinoma, 10 from prostatic adenocarcinoma, and 1 with metastatic foci from both tumors. The diagnosis of prostatic carcinoma was readily confirmed by immunostaining for prostatic-specific antigen, and prostatic acid phosphatase.

Conclusions: Mesorectal lymph node dissection provides prognostic information in rectal cancer, but careful examination may reveal other unsuspected pathology. Immunohistochemical staining is an essential tool in distinguishing the origin of a lymph node metastasis, especially when the histology does not look typical for rectal carcinoma. Moreover, these observations highlight the connection that can exist between mesorectal lymph node drainage, and extra mesorectal lymph nodes drainage.