Intraprostatic adipose tissue: a study of 427 whole mount radical prostatectomy specimens

Prostatic adenocarcinoma is the most frequently diagnosed cancer in American men. Tumor Gleason grade and stage provide extremely valuable prognostic information and play an important role in therapeutic decision making and patient counseling. A biopsy or radical prostatectomy specimen revealing carcinoma extending into extraprostatic tissue permits a T3 classification. This is most easily recognized, particularly in a needle biopsy, when tumor is seen to invade the adipose tissue. The existence of intraprostatic adipose tissue is somewhat controversial. To investigate this, formalin-fixed paraffin-embedded whole-mount radical prostatectomy specimens from 427 patients with adenocarcinoma were evaluated for intraprostatic adipose tissue. It was defined as any collection of adipocytes amid or internal to the most peripheral glands. The amount, anatomic location, and relationship to normal structures were also recorded. Intraprostatic adipose tissue was identified in 17 (3.98%) of cases. It consisted of small microscopic foci composed of 5 to 20 adipocytes. In 13 cases, the fat was intimately associated with benign glands. In another 2 cases, it was associated with small nerves, and in 2 cases was random with no specific localization. Intraprostatic adipose tissue was located in the peripheral zone in 15 cases and in the central zone in 2. Intraprostatic adipose tissue, although uncommon, does exist. Therefore, caution must be exercised in diagnosing extraprostatic extension based only upon identification of fat invasion, especially in a needle biopsy. The small size of foci of adipose tissue and its admixture with benign glands are useful morphologic clues in distinguishing it from extraprostatic fat.