Incidence of other primary cancers in 1,569 patients with pharyngolaryngeal cancer and treated with radiation therapy.

From January 1977 through December 1989, a total of 1,569 patients with pharyngolaryngeal cancer (oropharynx: 240, nasopharynx: 221, hypopharynx: 246, and larynx: 862) were treated at the Department of Radiology, Osaka University Hospital and the Department of Radiation Therapy, The Center for Adult Diseases, Osaka. The incidence of other primary cancers in these patients was investigated using the data base of radiation therapy combined with information from hospital-based and Osaka prefectural cancer registries. One hundred and seventy-six of the 1,569 patients (11%) had other primary cancers (oropharynx: 21%, nasopharynx: 7%, hypopharynx: 13%, and larynx: 9%). The time of development of other primary cancers in more than 50% of the cases ranged between one year before and one year after the diagnosis of primary pharyngolaryngeal cancer. The expected number of the second primary cancer was estimated by multiplying the age-sex specific incidence rates for Osaka residents with person-years at risk based on Osaka prefectural cancer registry data. The observed/expected (O/E) ratios were 3.17 (p less than 0.01) for oropharyngeal, 2.01 (p less than 0.01) for nasopharyngeal, 2.16 (p less than 0.01) for hypopharyngeal and 1.10 (n.s.) for laryngeal cancer. The most common sites of the second primary cancer in order of frequency were: the oral cavity and pharynx, esophagus and lung for oropharyngeal cancer, the oral cavity and pharynx for nasopharyngeal cancer, the oral cavity and pharynx and the esophagus for hypopharyngeal cancer and the oral cavity and pharynx, esophagus and lung for laryngeal cancer.