Sarcomatoid renal cell carcinoma. A study of its proliferative activity

Sarcomatoid renal cell carcinoma is an uncommon renal tumor consisting of carcinomatous and sarcomatous components. Although this tumor shows highly malignant biologic behavior, little is known about its proliferative activity.

Twelve surgically resected sarcomatoid renal cell carcinomas were analyzed in terms of cell proliferative activity and compared with three ordinary grades of renal cell carcinomas (12, Grade 1; 12, Grade 2; and 8, Grade 3). The analysis was achieved by a silver stain for nucleolar organizer regions (AgNOR) and immunohistochemical demonstration of proliferating cell nuclear antigen (PCNA) in formaldehyde-fixed paraffin-embedded sections.

The mean number of AgNOR in the nucleus of renal cell carcinoma was 1.5 +/- 0.2 (mean +/- standard deviation) for Grade 1, 2.6 +/- 0.3 for Grade 2, and 5.7 +/- 1.1 for Grade 3, but 7.8 +/- 2.0 was found for sarcomatoid renal cell carcinoma. The differences in the mean number of AgNOR per nucleus among the three grades and sarcomatoid renal cell carcinoma were statistically significant (P < 0.01). PCNA labeling indexes (positive nuclear ratio) were 4.8 +/- 2.7%, 19.8 +/- 5.6%, 37.8 +/- 6.6% in Grades 1, 2, and 3, respectively, and 45.5 +/- 13.3% in sarcomatoid renal cell carcinoma. The differences in the mean number of PCNA labeling indexes between Grades 1 or 2 and sarcomatoid renal cell carcinoma were statistically significant (P < 0.005). The AgNOR count correlated well with the reactivity of tumor cells for PCNA (correlation coefficient, 0.845; P < 0.01).

These findings suggest that sarcomatoid renal cell carcinoma is a highly proliferative renal cell carcinoma, which may be related to its aggressive biologic behavior.