Prostate Intraepithelial Neoplasia: A Premalignant Lesion

PIN, or Prostate Intraepithelial Neoplasia, is believed to be a likely precursor to full blown prostate cancer.

It is a proliferative lesion composed of prostate epithelial cells that are dividing more rapidly than normal epithelium; however, they are not yet becoming cancerous. In order to make the diagnosis a biopsy of the prostate must be performed and evaluated by a pathologist. The proliferating or rapidly growing cells within the normal glandular structures of the prostate show overlapping cells with enlarging nuclei and the prominence of nucleoli, blue-like dots within the prostate cells themselves.

It is generally believed that PIN does not influence serum PSA and, in fact, the amount of PSA produced by these abnormal cells is actually less than normal cells. The elevation of PSA in men with PIN is probably related to the coexistent unsampled prostate cancer which was missed by the prostate biopsy and ultrasound.

Ultrasound itself does not detect or image, in most cases, prostate cancer let alone able to visualize PIN. PIN is the most likely precursor of prostate cancer, and the presence of PIN on needle biopsy of the prostate indicates a higher than normal likelihood of developing prostate cancer in the future.

Anywhere between 40 and 60% of men with PIN will develop cancer of the prostate within two years, and therefore careful follow-up with recurrent biopsies on a six month basis is important. Studies suggest that most patients with PIN will develop overt cancer of the prostate within ten years.

Currently there are two types of PIN. The low-grade, or PIN-1, is of no clinical significance and probably has no relationship to cancer of the prostate. On the other hand, high-grade PIN, or PIN-2 and 3, appear to be the types that develop into cancer. There are no definitive treatments for PIN at this particular time. However, recent studies with tamoxifen and Casodex suggest that the malignant degeneration from PIN to cancer is slowed up and the incidence is decreased.

My belief is that in most cases of PIN there is also simultaneous coexisting cancer of the prostate which was not diagnosed at the time of biopsy, and the high incidence of cancer associated with PIN is due to the fact that the cancer already existed with the PIN at the time of the original biopsy, and additional biopsies will make the definitive diagnosis.

PIN is a very high predictor as a marker for prostate cancer, so its identification on biopsy specimens warrants close observation and recurrent biopsy. Followup biopsy of the prostate is suggested every three to six months for at least two years, and probably annually thereafter.

When physicians are doing the biopsies, it is suggested that saturation biopsies under anesthesia would be appropriate since the chances of diagnosing cancer is much higher with a greater number of cores of tissue obtained. Normally five to six cores of tissue are obtained, and when doing a saturation biopsy 18 to 25 cores can be obtained for a definitive diagnosis.