LAUSR

Importance The US cancer survivor population is rapidly growing. Cancer survivors are frequently excluded from cancer clinical trials and observational research. Objective To examine prevalence of prior cancer among individuals newly diagnosed with cancer. Design, Setting, and Participants Linked observations across the population-based Surveillance, Epidemiology, and End Results (SEER) program of cancer registries (1975-2013) for 740 990 persons newly diagnosed with cancer from January 2009 through December 2013. Prevalence of prior cancer was estimated by age (<65 years vs ≥65 years) and incident cancer type. Main Outcomes and Measures Prevalence of prior cancer was derived from SEER sequence numbers, which represent the order of all primary reportable tumors diagnosed in a lifetime. Incident cancers were categorized as: (1) first or only primary; (2) second order or higher primary in the same cancer site; and (3) second order or higher primary in a different cancer site. Results Of 765 843 incident cancers diagnosed between 2009 and 2013, 141 021 (18.4%) represented a second order or higher primary cancer. Overall, approximately one-fourth (25.2%) of older (≥65 years) and 11% of younger adults newly diagnosed with cancer had a history of prior cancer. Prevalence of prior cancer ranged from 3.5% to 36.9% according to incident cancer type and age, with most prior cancers diagnosed in a different cancer site. Conclusions and Relevance A substantial proportion of patients diagnosed with incident cancer in the United States have survived a prior cancer. These patients may be excluded from clinical trials and underrepresented in observational research, and little is known about their treatment and survivorship needs. Understanding the nature and impact of prior cancer is critical to improving clinical trial accrual and generalizability, disease outcomes, and patient experience.