Study design, Database and Case Identification
We conducted a retrospective cohort study using population-based data. Incidence of malignant neoplasms among infants (age <365 days) diagnosed between January 1, 1975 and December 31, 2014 were extracted from the SEER registry using the International Classification Childhood Cancer (ICCC-3)(11), 3rd Edition . Infant cancer cases were collected from 9 population-based cancer incidence registries (SEER 9) that provided continuing data for the 40-year observation period and represent approximately 10% of the U.S. population.(12) The registries include broad geographic and racial distributions of persons in the states of Connecticut, Hawaii, Iowa, New Mexico, and Utah and the metropolitan areas of Atlanta, Georgia; Detroit, Michigan; San Francisco-Oakland, California; and Seattle-Puget Sound, Washington. The raw data in our study were downloaded from the SEER website via SEER*Stat in client-server mode after we submitted a request for access and signed the SEER research data agreement.(12) This study was classified as exempt by the Institutional Review Board at the Baylor College of Medicine in Houston, Texas.
Numerators for incidence rates comprise the total number of cancer cases occurring among infants from 1975 to 2014. Denominators for calculation of incidence rates were population counts for infants aged <1 year in each of the 9 SEER programs included in this report. Since the number of cancers diagnosed per year among infants was often quite small, some trends were calculated after combining cases diagnosed in two-year. Race was grouped as white, black, and other. Approximately 96% of all cases were confirmed microscopically. Only infants diagnosed with malignant tumors were included in the analyses. Diagnoses were classified into 12 main tumor groups and 47 subgroups according to the ICCC version 3 (ICCC-3). These 12 groups were described as follows: (1) leukemia: leukemias, myeloproliferative and myelodysplastic diseases; (2) lymphoma: lymphomas and reticuloendothelial neoplasms; (3) CNS neoplasms: CNS and miscellaneous intracranial and intraspinal neoplasms; (4) neuroblastomas: neuroblastoma and ganglioneuroblastoma; (5) Sarcomas: soft tissue and other extraosseous sarcomas; (6) germ cell: ­germ cell tumors (GCTs), trophoblastic tumors, and neoplasms of the gonads; (7) Retinoblastoma: Retinoblastoma; (8) Hepatic tumor: Hepatic; (9) Renal tumors: Renal; (10) Bone: Malignant bone tumors; (11) Other and unspecified malignant neoplasms; and (12) other: other malignant epithelial neoplasms and malignant melanomas. Bone (10), other and unspecified (11) and other (12) tumors were excluded from analysis due to the small number of cases (<50).