Significant risk of second primary cancer among laryngeal squamous cell carcinoma patients even after 20 years

Background: Evidence on the risk of second primary cancer (SPC) following primary laryngeal squamous cell carcinoma (LSCC) is limited, especially in Europe. Methods: Patients diagnosed with primary LSCC from 1953–2018 were retrieved from the Finnish Cancer Registry. A total of 6241 LSCC patients were identified adding to 49,393 person-years (PY) of follow-up until the end of 2019. Only one patient emigrated and was lost to follow-up. Both standardized incidence ratios (SIR) and excess absolute risk (EAR) per 1000 person-years at risk (PYR) of second primary cancer (SPC) were calculated relative to the general population. Only non-laryngeal SPCs diagnosed six months after diagnosis of primary LSCC were included. Results: A SPC was diagnosed in 1244 LSCC patients (20% of all LSCC patients) over the 65-year period, predominantly in men (92%, n = 1170). Out of all SPCs, 34% were diagnosed within 0.5 to 5 years and 66% after 5 years from primary LSCC. Among male patients, the overall SIR for SPC at any location was 1.61 (95% CI: 1.52–1.71), corresponding to 9.49 excess SPCs per 1000 PYR (95% CI: 8.19–11). The corresponding SIR for women was 1.47 (95% CI: 1.15–1.84), yielding 4.82 excess SPCs per 1000 PYR (95% CI: 2.36–9.84). The risk remained significant even after 20 years of follow-up (SIR for all 1.73, 95% CI: 1.49–2.01 and EAR 16.8 per 1000 PY, 11.88–23.75). The risk for SPC was also significantly elevated in all age groups, except <40. The highest SIRs were for SPCs arising in the mouth/pharynx (SIR for all 3.08, 95% CI: 2.36–3.95 and EAR 0.80 per 1000 PY, 0.55–1.15) and lungs (3.02, 2.75-3.30 and 5.90 per 1000, 5.13–6.78). Conclusion: Patients with LSCC as primary cancer have a 60% excess risk for an SPC, especially for tobacco-associated cancers, remaining significantly elevated even decades after treatment.