Given the importance of correctly staging
renal cell carcinomas, specific guidelines should be in place for
tumor size measurement. While a standard means of renal
tumor measurement has not been established, intuitively,
tumor size should be based on fresh measurements. We sought to assess the accuracy of postfixation and microscopic measurements of renal
tumor size, as compared to fresh measurements and radiographic size. Thirty-four
nephrectomy cases performed by a single surgeon were prospectively measured at different time points. The study cases included 23 clear cell
renal cell carcinomas, 6 papillary
renal cell carcinomas, and 5 other renal
tumors. Radiologic
tumors were 12.1% larger in diameter than fresh
tumors (P<0.01). Furthermore, fresh specimens were 4.6% larger than
formalin-fixed specimens (P<0.01), and postfixation measurements were 7.1% greater than microscopic measurements (P<0.01). The overall mean percentage of shrinkage between fresh and histological specimens was 11.4% (P<0.01). Histological processing would cause a
tumor stage shift from pT1b to pT1a for two
tumors in this study. The shrinkage effects of
formalin fixation and histological processing may result in understaging of
renal cell carcinomas. The shrinkage factor should be considered when reporting
tumor size.