p16 and pRb immunohistochemical expression increases with increasing tumour grade in mammary phyllodes tumours

Aims: Control of cell cycling and proliferation is critical to the development of neoplasia and may play a role in the pathogenesis of phyllodes tumours (PTs). This study aimed to evaluate the immunohistochemical expression of certain proteins from the G1 ⁄ S transition of the cell cycle in a cohort of PTs, to determine their role in tumour pathogenesis and to identify any associations with patient outcome. Methods and results: Sixty-five PTs (34 benign, 23 borderline and eight malignant) diagnosed at a single institution between 1990 and 2006 were analysed. Immunohistochemistry for p16, pRb, cyclin D1 and Ki67 was performed. Expression of the following markers increased significantly with tumour grade: stromal nuclear and cytoplasmic p16 (P = 0.01 and 0.002, respectively), stromal and epithelial pRb (P = 0.000 000 06 and 0.004, respectively), and stromal and epithelial Ki67 (P = 0.03 and 0.04, respectively). Epithelial pRb scores of 7 (range 0–7) were significantly associated with reduced disease-free survival (DFS) compared with scores of <7 (P = 0.0009). No relationship was found between cyclin D1 expression in either the epithelium or the stroma, and grade or DFS. Conclusions: The results suggest that alterations at the G1 ⁄ S transition of the cell cycle play an important role in the progression of PTs.