The collapse of the World Trade Center (WTC) towers due to the terrorist attacks on September 11, 2001 created an unprecedented mixture of hazardous materials including known and suspected carcinogens including, but not limited to,  asbestos, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and dioxins. Three research centers that follow cohorts of rescue/recovery workers since the WTC disaster include: the Fire Department of the City of New York (FDNY); the Icahn School of Medicine at Mount Sinai (ISMMS); and the New York City Department of Health and Mental Hygiene (DOHMH). These centers have reported mostly non-significantly elevated cancer rates post-exposure to the WTC-site.  Challenges of determining the causal relationship between WTC exposure and cancer in rescue/recovery workers include: lack of individual-level exposure data for specific chemicals, different exposure ascertainment methodologies for the three cohorts, loss to follow-up, inadequate power for cohort-specific analyses, demographic heterogeneity between the cohorts, and the lack of a viable comparison cohort.