RB1 and squamous cell carcinoma: This category of tumors includes those with Rb loss at the gene level (such as Rb) and those with functional inactivation of Rb protein, such as squamous cell carcinomas of the oropharynx, cervix, and genital tract in which the E7 oncogene of HPV16 inactivates Rb (Wiest et al., 2002; Dickson, 2014).