inclusion criteria: - age ≥ 18 - ecog 0-3 - for patients who have not started radiation at the time of screening: patients are required to have a plan in place for a minimum of 10 radiation treatments with or without concurrent systemic therapy - for patients who have already started radiation at the time of screening: patients must complete enrollment such that they are able to receive at least 10 radiation treatments with hydroxychloroquine. - disease site - mandatory inclusion criteria: - no covid-19 symptoms within 14 days of enrollment: - (temp >38c in addition to sore throat, cough, wheezing, chest tightness, shortness of breath, body aches, chills, diarrhea, and anosmia) - if symptoms are present within 14 days of enrollment, patients with a negative covid-19 pcr or covid-19 serology assay are eligible for inclusion. - no close contact with confirmed covid-19 person - close contact defined as: - within 6 feet for prolonged period - cohabitating - optional laboratory criteria (recommended if available) - negative pre-treatment sars-cov-2 rapid antigen test result (within 1 week of enrollment) - negative pre-treatment sars-cov-2 pcr test result (within 1 week of enrollment) using mskcc laboratory or outside laboratory assay - negative pre-treatment standard q covid-19 igm/igg rapid serology result (within 1 week of enrollment) - blood serum for sars-cov-2 serology tests (being validated by mskcc) - disease site meets following criteria: - head and neck / high-risk skin cancer - lung cancer - breast cancer - prostate cancer - central nervous system tumors - gastrointestinal system cancer - gynecologic cancer - other disease sites permitted at pi discretion

inclusion criteria: - age ≥ 18 - ecog 0-3 - for patients who have not started radiation at the time of screening: patients are required to have a plan in place for a minimum of 10 radiation treatments with or without concurrent systemic therapy - for patients who have already started radiation at the time of screening: patients must complete enrollment such that they are able to receive at least 10 radiation treatments with hydroxychloroquine. - disease site - mandatory inclusion criteria: - no covid-19 symptoms within 14 days of enrollment: - (temp >38c in addition to sore throat, cough, wheezing, chest tightness, shortness of breath, body aches, chills, diarrhea, and anosmia) - if symptoms are present within 14 days of enrollment, patients with a negative covid-19 pcr or covid-19 serology assay are eligible for inclusion. - no close contact with confirmed covid-19 person - close contact defined as: - within 6 feet for prolonged period - cohabitating - optional laboratory criteria (recommended if available) - negative pre-treatment sars-cov-2 rapid antigen test result (within 1 week of enrollment) - negative pre-treatment sars-cov-2 pcr test result (within 1 week of enrollment) using mskcc laboratory or outside laboratory assay - negative pre-treatment standard q covid-19 igm/igg rapid serology result (within 1 week of enrollment) - blood serum for sars-cov-2 serology tests (being validated by mskcc) - disease site meets following criteria: - head and neck / high-risk skin cancer - lung cancer - breast cancer - prostate cancer - central nervous system tumors - gastrointestinal system cancer - gynecologic cancer - other disease sites permitted at pi discretion