PIN
Meaning of PIN: Visible only under a microscope, it produces no lump, no symptom and no change in a blood test result.
Definition of PIN
PIN, or prostatic intraepithelial neoplasia, is an abnormal growth pattern in the cells lining the small glands inside the prostate. The cells look abnormal but stay within the gland's own boundary, so PIN is not cancer. It is found only when prostate tissue is examined under a microscope, usually by chance.
What does the pathologist actually see?
Normal prostate glands are lined by two layers: a surface layer of secretory cells and a continuous basal layer beneath them. In PIN the surface cells become crowded and irregular, with enlarged nuclei and prominent internal dots called nucleoli, which is the same kind of change seen in cancer. What separates the two is the basal layer. In PIN it is still there, at least in part, so the abnormal cells remain confined inside the existing gland outline. In invasive cancer the basal layer is gone and the cells have broken out into surrounding tissue. Special stains that mark basal cells are used when the distinction is not obvious.
What do low grade and high grade mean?
| Grade | Appearance | How it is handled in reporting |
|---|---|---|
| Low grade | Mild crowding and variation in the cells | Pathologists agree poorly on it and it carries no established significance, so many laboratories no longer report it |
| High grade | Marked crowding with clearly enlarged nucleoli, still inside the gland outline | Reported, since it is recognized as a precursor change and turns up alongside cancer more often than chance would predict |
What follows a report of high grade PIN?
It is not a cancer biopsy result and it does not carry a stage the way stage I prostate cancer does. Its significance has also narrowed over time. When biopsies sampled only a few sites, finding high grade PIN meant cancer was often missed nearby and repeat sampling frequently found it. With the far more extensive sampling now standard, a single focus of high grade PIN is followed by cancer on repeat biopsy only slightly more often than a fully benign result. Several separate foci across different cores carry more weight than one. PIN itself produces nothing detectable: it causes no urinary symptoms, forms no palpable lump and does not raise the blood marker used in prostate screening. The concept parallels cervical intraepithelial neoplasia, where abnormal cells are likewise confined to the surface layer, although the two differ greatly in how reliably they progress.
Also known as
Used in a sentence
The prostate biopsy identified an area of high-grade PIN without evidence of invasive carcinoma.
Good to know
PIN is a noncancerous finding rather than a cancer diagnosis, and only the high-grade form is generally considered to warrant closer follow-up for possible coexisting prostate cancer.