Expression of p63, CD10, and Ki-67 in giant cell tumor of bone: A diagnostic immunohistochemical study

Giant cell tumor of bone (GCTB) is a locally aggressive tumor driven by neoplastic mononuclear stromal cells. Stromal immunophenotyping may support diagnosis in giant cell-rich mimics and provide insight into tumor biology. Archival formalin-fixed, paraffin-embedded tissue samples from 31 GCTB cases diagnosed between 2015 and 2025 were studied and reviewed by consultant pathologists on-site and remotely to confirm the diagnosis and assess stromal atypia and mitoses. Immunohistochemistry for p63, cluster of differentiation 10 (CD10), and Ki-67 was performed and interpreted in stromal cells only; p63 and CD10 expression were categorized as low or high, and Ki-67 labeling index (LI) was grouped using a 10% cutoff. Available clinical variables included age, sex, anatomical site, tumor size, and recurrent-case status. Recurrent-case status was based on documentation at presentation or referral, not on prospectively confirmed recurrence. The mean age was 42.5 ± 15.4 years; 16/31 cases (51.6%) were female. Recurrent-case status was recorded in 14/31 cases (45.2%). High p63 and CD10 expression were observed in 20/31 cases (64.5%) and 22/31 cases (71.0%), respectively. In univariate analysis, CD10-high expression was associated with recurrent-case status (P = .021), while p63-high expression showed a borderline association (P = .057). Ki-67 LI was not associated with recurrent-case status (P = .389). p63 expression correlated significantly with CD10 expression (P = .003) and with higher Ki-67 LI. Stromal p63 and CD10 were commonly expressed in GCTB. CD10-high expression was associated with recurrent-case status in univariate analysis, but this exploratory finding should not be interpreted as recurrence prediction.