Diagnostic utility of Ki-67 proliferation index, PSA, and other immunohistochemical markers in prostatic basal cell carcinoma: A review of 24 cases in the current literature and discussion on current treatment and diagnostics

Background Basal cell carcinoma (BCC) of the prostate is a rare and poorly characterized malignancy distinct from conventional prostatic adenocarcinoma. Due to its rarity, diagnostic challenges arise, often leading to misclassification and delayed management. Immunohistochemical markers such as Ki-67 proliferation index and prostate-specific antigen (PSA) levels may aid in distinguishing BCC from typical adenocarcinoma, but data remain limited. Methods This case series review study retrospectively analyzes published case reports and series spanning from 1988 to 2023 to evaluate Ki-67 staining patterns, PSA levels, and other immunohistochemical features to identify distinguishing characteristics of prostatic BCC. Data extracted included patient demographics, PSA levels at presentation, Ki-67 proliferation index values, and results of other immunohistochemical staining (i.e., PSA, P63). Results Of the 24 BCC cases included in the final analysis, 20 reported PSA level at first presentation (mean: 2.56 ng/mL, range 0.08-7.3 ng/mL, normal range <4), 15 reported PSA IHC staining, and only 13 reported Ki-67 percentage values obtained through primary tumor biopsy staining (mean: 46.88%, range 0-80%). In comparison, Ki-67 expression numbers from National Comprehensive Cancer Network (NCCN) for prostate adenocarcinoma report varied Ki-67 expressions between risk groups: low-risk patients averaged 5.1% ± 3.8%, intermediate-risk patients averaged 7.4% ± 6.8%, and high-risk patients averaged 12.0% ± 12.4%. Various immunohistochemical staining was also collected yielding positive staining with Ki-67 in 13/13 cases, HMWCK/34βE12 in 14/14 cases, P63 in 14/14 cases, and BCL-2 in 12/13 cases. Conclusion This retrospective analysis suggests that prostatic BCC may be characterized by higher Ki-67 proliferation indices and lower PSA levels compared to typical prostatic adenocarcinoma. This review further explores and proposes the potential of combining Ki-67 and PSA assessments along with other biomarkers to aid in distinguishing BCC from conventional prostate cancers, facilitating earlier recognition and appropriate management of this rare malignancy.