Subsequent malignant neoplasm among cancer survivors in the United States.

BACKGROUND: One of the most significant events following a diagnosis of cancer is the diagnosis of subsequent malignant neoplasm (SMN). Estimates of the number and risk of more than one malignancy in this population are needed. METHODS: Utilizing data from 1975 to 2021 from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program, estimates of the number, proportion, and standardized incidence ratios (SIRs) of survivors with SMN by age at diagnosis, time since diagnosis, and primary site were calculated. RESULTS: As of January 1, 2022, the estimated number of cancer survivors in the US with one malignancy was 14,940,581, while 2,191,482 survivors had two malignancies. A smaller number of survivors (379,897) had three malignancies; 110,859 people had four or more malignancies. Compared to people who never had cancer, cancer survivors had an increased risk of SMN (SIR, 1.19; 95% CI, 1.19 to 1.19). Survivors diagnosed with the first malignancy before age 40 were at highest risk of SMN (SIR, 1.78; 95% CI, 1.76 to 1.81). Among all cancer survivors, 15.2% had an SMN, with the highest percentage of survivors with SMN observed among those with a history of melanoma, bladder cancer, or Hodgkin lymphoma. CONCLUSION: More than 2.5 million cancer survivors in the US have had two or more malignancies, representing 15% of the US cancer survivor population. The risk of SMN is notable for those diagnosed at a younger age and with certain types of first malignancies. IMPLICATIONS FOR CANCER SURVIVORS: About 15% of cancer survivors in the United States have had more than one malignancy.