Carolyn C. Compton

Serous cystic tumors of the pancreas are unique among pancreatic cystic neoplasms in that they are almost always cytologically monomorphous and biologically benign. The diagnostic challenge for the surgical pathologist is to recognize the spectrum of architectural variation that may lead to misdiagnosis, either preoperatively or postoperatively, and the additional lesions and conditions with which serous tumors may be associated.

Surgical resection is the primary treatment modality for colorectal cancer, and the most powerful tool for assessing prognosis following surgery is pathologic analysis of the resection specimen. Although the parameters that determine the pathologic stage are the strongest predictors of postoperative outcome, a number of additional pathologic features have prognostic significance that is independent of stage. These include: histologic grade; small vessel (lymphatic or venular) invasion; extramural venous invasion; perineural invasion; tumor border configuration; host lymphoid response to tumor, and the status of surgical margins. For specimens in which the radial (circumferential) margin is applicable, surgical clearance around the tumor is also of import. It is self-evident that, compared to data derived from additional assays, prognostic information that can be derived directly from standard histologic sections of a tumor is of the greatest cost-benefit to the patient. In the current era of cost containment, it is essential that surgical pathologists evaluate and report the pathologic features that are of prognostic and/or predictive significance in every case of colorectal cancer and, in turn, that the import of these be understood by the treating physicians.

This study examines the association between the pathologic response of rectal cancer after irradiation and its pretreatment proliferative state as assayed by proliferating cell nuclear antigen (PCNA) and mitotic activity. Ninety patients with clinical stage T3 and T4 rectal cancer received preoperative irradiation followed by surgery. Pretreatment tumor biopsies were scored for PCNA activity (number of tumor cells staining immunohistochemically with an anti-PCNA monoclonal antibody) and the number of mitoses per 10 high-powered fields (hpf). Postirradiation surgical specimens were examined for extent of residual disease. The tumors of 33 of 90 patients (37%) exhibited marked pathologic downstaging (no residual tumor or cancer confined to the rectal wall) after preoperative irradiation. Two features were independently associated with the likelihood of marked pathologic regression after preoperative irradiation: lesion size and PCNA/mitotic activity. When stratified by tumor size, marked tumor regression occurred most frequently in smaller tumors with high PCNA/mitotic activity compared with larger tumors with lower PCNA/mitotic activity. Intermediate downstaging rates were seen for small or large tumors with moderate PCNA/mitotic activity. Tumor PCNA/mitotic activity predicts the likelihood of response to irradiation, which may aid in formulating treatment policies for patients with rectal cancer.