Second primary cancers in patients with a pharyngeal index tumour: a register-based cohort study

Background: While prior research on the SPC (second primary cancer) risk among pharyngeal carcinoma (PC) patients has been conducted in other regions, the European perspective is underrepresented. Our register-based cohort study aims to assess the subsite-specific risk of SPC among individuals initially diagnosed with a pharyngeal index tumour. Methods: Standardized incidence ratios (SIR) of SPC were calculated relative to the general population for all patients diagnosed with a primary oropharyngeal, nasopharyngeal, and hypopharyngeal carcinoma (OPC, NPC, and HPC) in Finland during 1953–2021. Results: A total of 4701 PC patients – 3320 men (71%) and 1381 women (29%) – were identified. The average and median follow-up times were 5.7 and 2.8 years, respectively. A SPC was diagnosed in 561 patients (11.9%): in 12.3% of men (n = 410) and 10.9% of women (n = 151). For male PC patients, the overall SIR for an SPC at any primary site was 1.83 (95% CI: 1.65–2.01). For female patients, the corresponding SIR was 1.89 (95% CI: 1.60–2.22). OPC and HPC showed increased risks for SPCs of the mouth/pharynx (SIR 4.41 and 6.91, respectively) and respiratory organs (SIR 3.51 and 4.80). OPC patients also had an increased risk in digestive organs (SIR 1.83). Male NPC patients exhibited increased risks for oral/pharyngeal, brain, and haematolymphoid SPCs (SIRs 5.14, 6.60, and 3.05, respectively). Conclusion: PC patients face an 80% higher SPC risk, which persists decades after treatment. Healthcare professionals must be aware of this, providing counselling and encouraging a healthy lifestyle, including smoking cessation, while monitoring symptoms.