What does Focal Atypical Small Acinar Proliferation (FASAP) in prostate biopsy results indicate?

Focal Atypical Small Acinar Proliferation (FASAP) in Prostate Biopsy Results

Focal Atypical Small Acinar Proliferation (FASAP) is a concerning pathological finding that indicates suspicious small glandular structures that have some but not all features of prostate cancer, requiring prompt follow-up with repeat biopsy due to a high risk (approximately 50%) of underlying prostate cancer.

What is FASAP?

• FASAP is characterized by small single-cell layer acini that lack a basal cell layer, distinguishing it from High-Grade Prostatic Intraepithelial Neoplasia (HGPIN) 1
• It represents suspicious glandular structures that have some features of adenocarcinoma but insufficient criteria for a definitive cancer diagnosis 1
• FASAP is reported in approximately 3-5% of all prostate biopsies 1, 2
• Unlike HGPIN (which is a distinct pathologic diagnosis), FASAP represents one of two possibilities: normal prostate tissue distorted by artifact or prostate cancer that doesn't meet the full histologic criteria for diagnosis 1

Diagnostic Confirmation

• FASAP diagnosis is often confirmed through immunohistochemical staining for basal cell markers and markers of neoplasia such as Alpha Methyl-Acyl CoA Racemase (AMACR) 1, 3
• The diagnosis represents uncertainty in the pathology report, as findings might represent non-cancerous pathology mimicking cancer or an under-sampled prostate cancer site 4

Clinical Significance and Cancer Risk

• FASAP confers a high risk of prostate cancer on subsequent biopsy, with positive rebiopsy rates of 50% or more 1
• Studies show cancer detection rates of 34-50% on repeat biopsy following FASAP diagnosis 2, 5
• The most likely area of finding cancer resides in the prostate area showing atypia 1
• In one study, 100% of patients with FASAP who underwent immediate radical prostatectomy had a final pathological diagnosis of adenocarcinoma 6

Management Recommendations

• NCCN guidelines strongly recommend a repeat extended biopsy scheme within 3-6 months of an initial FASAP diagnosis 1
• Additional cores should be obtained specifically from the region demonstrating atypia 1
• If no cancer is found on the repeat biopsy, close follow-up with PSA (and consideration of complementary DRE) is recommended 1
• Higher PSA levels are associated with increased risk of identifying prostate cancer on repeat biopsy 2

Grading of Cancer Found After FASAP

• Most cancers found after FASAP diagnosis are low-grade (Gleason 6 or lower), but high-grade disease cannot be excluded 2, 4
• In one multi-institutional study, of those diagnosed with subsequent prostate cancer after FASAP:
  • 78% had Gleason 3+3 disease
  • 17% had Gleason 7 disease
  • 6% had Gleason 8-10 disease 2

Potential Pitfalls in Management

• Delaying or omitting repeat biopsy may miss significant cancer in some patients 1, 5
• The average time to repeat biopsy is often longer than recommended (246 days in one study vs. the recommended 90-180 days) 5
• Some recent studies suggest that immediate repeat biopsy might represent overtreatment in some cases, as only 8% of patients with FASAP were found to have high-grade disease on follow-up 2
• No reliable clinical or pathological factors can definitively predict which patients with FASAP will have cancer on repeat biopsy 4

Summary of Management Approach

1. Confirm FASAP diagnosis with expert pathology review and appropriate immunohistochemical staining 1, 3
2. Schedule repeat extended biopsy within 3-6 months 1
3. Ensure additional sampling of the area where FASAP was identified 1
4. If cancer is found, proceed with appropriate treatment based on grade and stage 1
5. If no cancer is found, continue close monitoring with PSA testing and consider additional biopsies if PSA rises 1