A transcription factor known as FOXA1 may help pathologists identify aggressive forms of prostate cancer that frequently lose conventional diagnostic markers, according to a new study published in Histopathology.
Researchers from The University of Texas MD Anderson Cancer Center and Johns Hopkins Hospital found that FOXA1 showed high sensitivity for prostate adenocarcinoma and remained detectable in many cases of small cell carcinoma of the prostate — a rare but highly aggressive neuroendocrine subtype that often emerges after hormonal therapy resistance develops.
Small cell carcinoma of the prostate presents a major diagnostic challenge because tumor cells commonly lose expression of traditional prostate markers such as prostate-specific antigen (PSA), prostate-specific membrane antigen (PSMA), androgen receptor (AR), and NKX3.1. This can make it difficult to determine whether metastatic neuroendocrine tumors originated in the prostate or arose from another organ.
To identify potential new biomarkers, investigators analyzed gene-expression data from The Cancer Genome Atlas across 31 tumor types and identified FOXA1 as highly expressed in prostate cancer tissue. They then evaluated FOXA1 protein expression using immunohistochemistry in primary and metastatic prostate tumors as well as a wide range of other malignancies.
FOXA1 demonstrated strong diagnostic performance in conventional prostate cancer, with positive staining observed in 76 of 81 primary prostate adenocarcinomas and all 11 metastatic adenocarcinomas examined. The staining pattern closely resembled that of NKX3.1, a commonly used prostate-specific marker.
The most clinically significant findings involved small cell carcinoma of the prostate. FOXA1 expression persisted in 80 percent of primary small cell carcinomas and 57 percent of metastatic cases, despite complete loss of conventional prostate markers in many tumors.
In one representative case described in the study, a prostate biopsy contained both adenocarcinoma and small cell carcinoma components. FOXA1 staining was present in both tumor types, whereas NKX3.1, PSMA, and AR expression disappeared in the small cell component. Neuroendocrine markers, including chromogranin and synaptophysin, remained strongly positive.
The authors noted that FOXA1 may be particularly useful in evaluating metastatic neuroendocrine tumors in patients with a prior history of prostate cancer, where identifying the tissue of origin is often difficult. Positive FOXA1 staining could help support a prostatic origin in diagnostically ambiguous cases.
The investigators concluded that FOXA1 could serve as a valuable adjunct immunohistochemical marker in surgical pathology practice, particularly for aggressive and treatment-resistant prostate cancers. They added that larger validation studies will be needed to confirm the marker’s clinical utility and explore its potential role in prognostic stratification and targeted therapy development.
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