4-Point Therapy Response Score With PET/CT for Anal Squamous Cell Cancer

Inclusion Criteria: * Histologically confirmed biopsy proven invasive SCCA (any T, any N) deemed a candidate to undergo standard of care definitive chemoradiation at MD Anderson Cancer Center (MDACC) with curative intent * Age \> 18 years at time of study entry * Ability to provide written informed consent Exclusion Criteria: * Patients unwilling to participate in a PET/CT at baseline and at 3 months post completion of definitive chemoradiation * Patients with an active second primary malignancy requiring chemotherapy or radiation treatment * Stage IV SCCA