Incidence of AIDS-defining Illness by Cancer Status in an Observational Study among Medicaid Beneficiaries Living with HIV in the United States, 2001 - 2015.

BACKGROUND: Malignant neoplasms remain one of the leading morbidities and causes of death among people with HIV (PWH). Prior research suggests that certain cancer treatments may have deleterious effects on the immune system. SETTING: We quantified the relationship between non-AIDS-defining cancers (NADC) and the development of a new AIDS-defining illness (ADI) among PWH in Medicaid. We assembled a cohort of 154,493 Medicaid beneficiaries aged 18-64 with HIV from 14 US States between 2001-2015, with no evidence of a prevalent ADI or cancer. METHODS: We estimated incidence rates of first ADI among PWH who did and did not develop NADC. NADC status was time-updated, allowing individuals to contribute person-time before and after cancer diagnosis. We compared rates across NADC status by estimating adjusted incidence rate ratios (IRRs) using Poisson regression, controlling for sex, race/ethnicity, age, calendar year, and US state. RESULTS: PWH contributed 409,157 person-years, 3,843 incident NADCs, and 28,875 ADIs, resulting in an overall incidence rate of 7.06 ADIs per 100 person-years (among those without cancer: 6.9, 95% confidence interval (CI): 6.82, 6.98; after cancer diagnosis: 15.52, 95% CI: 14.66, 16.43). The adjusted IRR of ADIs after cancer diagnosis was elevated for all NADCs (2.82, 95% CI: 2.63, 3.02) and specific cancers (lung, colon, breast, and prostate). CONCLUSION: Incidence of new ADIs was elevated after cancer diagnosis. PWH undergoing cancer treatment may require careful observation for ADI development and potentially warrant consideration of immune-sparing cancer treatment regimens given prior data suggesting sustained decreases in CD4 cell counts after cancer treatment.