Second primary cancer following primary oral squamous cell carcinoma: a population-based, retrospective study

Background: Second primary cancer (SPC), defined as a metachronous solid cancer resulting from neither a recurrence of the primary cancer nor a metastasis, is a leading long-term cause of death for survivors of primary oral squamous cell carcinoma (OSCC). This study examined the risk of SPC following treatment of primary OSCC. Materials and Methods: This semi-national, population-based, retrospective study included all patients with primary OSCC treated with curative intent in Eastern Denmark in 2000–2014. The presence of SPC was confirmed from medical records and the Danish Pathology Data Bank. The rate of SPC was compared to the occurrence of any cancer in the Eastern Danish population using data from the Danish Cancer Registry. Results: A total of 936 patients with primary OSSC were enrolled. Of these, 219 patients (23%) were diagnosed with SPC during the follow-up (median 8.9 years, IQR: 5.4–12.6 years). The rate of SPC was four times higher than the occurrence of any cancer among the Eastern Danish population i.e., with a standardized incidence ratio (SIR) of 4.13 (95%CI: 3.55–4.80). SPCs were most frequently found in head and neck region (n = 97, SIR = 43.6), lower respiratory organs (n = 38, SIR = 5.6) and gastrointestinal organs (n = 33, SIR = 3.2) with increased SPC rates in all locations. Among patients who developed SPC within the study period the median time from OSCC to the first SPC was 4.4 years (IQR: 2.5–6.2). Significant associations were found between both smoking and excessive alcohol consumption after treatment of OSCC and the risk of SPC. Conclusions: A noteworthy increased rate of SPC following treatment of primary OSCC was found, especially in the head and neck region and in the lungs. Healthcare professionals should be aware of this increased risk.