Atypical small acinar proliferation (ASAP) of the prostate gland

Jason Wasserman MD PhD FRCPC and Trevor Flood MD FRCPC
January 20, 2025

Atypical small acinar proliferation (ASAP) is a term pathologists use when examining a prostate biopsy under a microscope. It describes a small group of atypical prostate glands that could represent reactive features, benign (noncancerous) entities, or low grade prostate cancer. The microscopic features of ASAP are insufficient to establish a definitive cancer diagnosis, although it is considered a finding that requires further evaluation.

Is atypical small acinar proliferation (ASAP) a cancerous or precancerous condition?

ASAP is not cancer and is not considered a precancerous condition by itself. Instead, it is a finding that may indicate the presence of cancer nearby or in unsampled areas of the prostate. However, it is important to remember that most men with ASAP will not have prostate cancer, and the majority of cancers found on repeat biopsy after an ASAP diagnosis are small, low grade (Gleason 6), and unlikely to cause serious harm.

Is atypical small acinar proliferation (ASAP) associated with an increased risk of developing prostate cancer?

Yes, men diagnosed with ASAP are at a higher risk of being diagnosed with prostate cancer on a repeat biopsy. Studies show that approximately 31% of men with ASAP will be found to have cancer when the biopsy is repeated. However, most of these cancers are low grade (Gleason 6), and the tumor found is typically small. Only a very small number of men (6% in one study) are found to have higher-grade (Gleason 7 or higher) cancer.

This means that although ASAP may signal an increased risk of prostate cancer, the majority of cancers found in this situation are considered clinically insignificant, meaning they are less likely to grow or spread.

What causes atypical small acinar proliferation (ASAP)?

The exact cause of ASAP is not always clear, but it is thought to arise from early changes in the prostate glands that may be related to cancer development. Age, genetics, and prostate-specific antigen (PSA) levels may play a role, but no specific cause has been identified.

What are the microscopic features of atypical small acinar proliferation (ASAP)?

Under the microscope, ASAP appears as a small cluster of unusual prostate glands. These glands may show some features of cancer, such as irregularly shaped cells or crowded glands, but they do not meet all the criteria for a diagnosis of cancer.

What is the treatment for atypical small acinar proliferation (ASAP) on a prostate biopsy?

The most common recommendation after a diagnosis of ASAP is to perform a repeat prostate biopsy. However, recent research shows that the majority of cancers found in men with ASAP are low grade and low volume. For this reason, not all men with ASAP need an immediate repeat biopsy within 6 months.

Your doctor may consider factors such as your PSA levels, overall health, and risk factors for prostate cancer when deciding on the timing of a repeat biopsy. Some men may benefit from advanced imaging techniques, like multiparametric MRI, to guide future biopsies and identify areas of concern more precisely.