Prostatic microcarcinomas in relation to cancer origin and the evolution to clinical cancer

In the prostate there is a uniquely high prevalence of microcarcinomas relative to larger cancers. The probability of metastasis has been found to correlate closely with increasing cancer volume. It is important to explore the relationship of microcarcinomas to these larger clinically significant cancers by comparing their histologic features and to trace their relationship to dysplasia, a proposed precursor lesion.

The histologic features of 107 microcarcinomas were related to associated dysplasia lesions. Their histologic grade was quantitated and compared with the quantitative grade and volume distribution of 100 incidental autopsy cancers and 209 clinical cancers from radical prostatectomy.

Microcarcinomas were contiguous with dysplasia foci in 81% of the cases, and evidence of cancer origin was found in 48%. Only 3 of 107 microcarcinomas had Grade 4 (poorly differentiated) areas. Grade 4 frequency and extent increased with cancer volume, and the relationship was similar between the autopsy and prostatectomy series. Metastasis was found only with cancers larger than 4 cc and having Grade 4 areas.

The majority of prostatic microcarcinomas appeared to arise from dysplasia. Only 3% of these early cancers showed areas of high histologic grade. In the autopsy and clinical series, it appeared that poorly differentiated areas evolve from low-grade cancer with time and increasing volume. Probability of metastasis was a function of volume and grade.