CD34 and p16 expression in central nervous system solitary fibrous tumors: an exploratory clinicopathologic study

Central nervous system solitary fibrous tumors (CNS SFTs) are rare mesenchymal neoplasms. The 2021 World Health Organization (WHO) classification recognizes a single SFT entity characterized by NAB2::STAT6-associated biology. This study evaluated clinicopathologic and immunohistochemical features, with particular emphasis on STAT6, CD34, and p16 expression.

We retrospectively reviewed 25 CNS SFTs identified between 2004 and 2024. Clinical, radiologic, histologic, immunohistochemical, treatment, and outcome data were collected. Histologic slides were reviewed by two neuropathologists. Immunohistochemistry for STAT6, CD34, and p16 was performed; molecular testing was unavailable.

The cohort included 13 men and 12 women, with a mean age of 51 years. Among tumors with available site data, most were intracranial. WHO grades were grade 1 in 40%, grade 2 in 24%, and grade 3 in 36%. Nuclear STAT6 expression was present in all cases. CD34 expression was greatest in grade 1 tumors, whereas p16 expression was numerically highest in grade 3 tumors; neither marker showed a statistically significant association with recurrence. Tumor size increased across WHO grades. Outcome analyses were limited by few events and heterogeneous follow-up.

CNS SFTs are clinicopathologically heterogeneous. STAT6 was a consistent diagnostic marker in this cohort. CD34 and p16 showed grade-related numerical patterns, but their prognostic value was not established. Larger, molecularly confirmed cohorts with standardized long-term follow-up are required.