By: Dan Sperling

Prostate biopsies occasionally detect cells with abnormal features, but they are not cancerous. Three types of unusual cells are considered to have the potential to become malignant.

Prostatic intraepithelial neoplasia (PIN)

“Neoplasia” comes from two Greek words: neos (new) and plassein (mold). In other words, some healthy prostate cells have developed in a new (abnormal) way. However, benign (noncancerous) neoplasia does not usually cause a rise in PSA, nor can it be seen under ultrasound. PIN is diagnosed as an incidental result of a prostate biopsy, occurring in anywhere from 9-14% of biopsies[i]. The neoplastic cells are identified under a microscope, but unlike cancer cells, they don’t seem to have grown or spread into surrounding healthy tissue. The pathologist (person who analyzes the tissue samples) usually classifies what he sees as either low-grade PIN (not very different from normal cells) or high-grade PIN (quite distinct from normal cells but not cancerous).

It is not uncommon for low-grade PIN to develop even when a man is in his twenties. The relationship of low-grade PIN to prostate cancer is unclear. Patients who are diagnosed with low-grade PIN are generally not advised to do anything about it.  On the other hand, the presence of high-grade PIN is considered predictive of cancer, with a probability of developing cancer within 10 years.[ii] If high-grade PIN is found by biopsy, there is about a 20%-30% probability that cancer cells already exist somewhere in the prostate. Thus, men with hi-grade PIN are usually advised by their doctors to monitor their prostate. Without a diagnosis of cancer, there is no treatment recommended for PIN, regardless of grade.

Atypical small acinar proliferation (ASAP)

This is sometimes just called atypia. It is a term used to describe unusual looking cells when no other diagnosis is clear. In ASAP, the cells look like they might be cancerous when viewed under the microscope, but there are too few of them to be sure. If ASAP is found, there’s a high chance that cancer is also present in the prostate, which is why many doctors recommend getting a repeat biopsy within a few months. Although ASAP is found in only 2% of biopsies, up to 60% of patients with an initial finding of ASAP are subsequently diagnosed with prostate cancer.[iii]

Proliferative inflammatory atrophy (PIA)

Chronic inflammation in tissues such as the liver, bladder and large bowel have been observed to eventually become cancer. The prostate can also develop chronic inflammations; under certain conditions, the inflamed cells begin to divide more rapidly. There appears to be a link between such proliferation, called proliferative inflammatory atrophy (PIA), and cells mutating into prostate cancer. In PIA, the prostate cells look smaller than normal. It is estimated that areas of the gland with PIA are 20% more likely to become malignant.[iv]

In all three conditions, physicians recommend repeat biopsies. However, multiparametric MRI may be useful to monitor for the development of lesions, and to guide targeted biopsies as a way to avoid overdetection that may subsequently lead to overtreatment.

[i] Bostwick DG, Liu L, Brawer MK, Qian J. High-Grade Prostatic Intraepithelial Neoplasia. Rev Urol. 2004;6(4):171-179.

[ii] Ibid. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1472840/

[iii] Bostwick D and Meiers I. Atypical small acinar proliferation in the prostate. Arch Pathol Lab Med. 2006(Jul);130:952-57.

[iv] Canadian Cancer Society https://www.cancer.ca/en/cancer-information/cancer-type/prostate/prostate-cancer/precancerous-conditions/?region=bc