Population-based risk assessment of second primary cancers following a first head and neck cancer: patterns of association and difficulties of its analysis.

PURPOSE The diagnosis of a second primary cancer (SPC) is a major concern in the follow-up of survivors of a primary head and neck cancer (HNC), but the anatomic subsites in the head and neck area are close, making it difficult to distinguish a SPC of a recurrence and therefore register it correctly. METHODS We performed a retrospective cohort study using data from two population-based cancer registries in Catalonia, Spain: the Tarragona Cancer Registry and the Girona Cancer Registry. All patients diagnosed with HNC during the period 1994-2013 were registered and followed-up to collect cases of SPC. We analysed the standardized incidence ratio (SIR) and the excess absolute risk (EAR) to determine the risk of second malignancies following a prior HNC. RESULTS 923 SPC were found in a cohort of 5646 patients diagnosed of a first head and neck cancer. Men had an increased risk of a SPC with a SIR of 2.22 and an EAR of 216.76. Women also had an increased risk with a SIR of 2.02 and an EAR of 95.70. We show the risk for different tumour sites and discuss the difficulties of the analysis. CONCLUSION The risks of a SPC following a prior HNC in Tarragona and Girona are similar to those previously found in other similar cohorts. It would appear to be advisable to make a revision of the international rules of classification of multiple tumours, grouping the sites of head and neck area with new aetiological criteria to better determine and interpret the risks of SPC obtained in these studies.