PARP1 and head and neck squamous cell carcinoma: While all cells exhibited an increase in γh2AX and PARP1 cleavage, indicating that estrogen induces DNA damage that results in an increase of apoptosis, no significant alterations in pRb were observed in any of our HPV+HNSCC lines, and p53 was significantly increased only in SCC47 and UMSCC104 cells.