Second primary cancer risk and survival in prostate cancer patients: A nationwide analysis

Different treatments for prostate cancer (PC) could affect a patient's risk of developing second primary cancers (SPCs). We assessed the incidence of SPC and overall survival (OS) after SPC diagnosis in patients with PC who underwent radical prostatectomy (RP) or radiation therapy (RT) as primary treatment.

Using the National Health Insurance Service database in South Korea, all male patients with PC between 2002 and 2018 were corrected for selection bias between the RT and RP groups by inverse probability of treatment weighting. The primary outcome was the incidence of SPC, and secondary outcome was OS after SPC diagnosis; cumulative incidence functions for competing risks of each SPC type were evaluated between the RP and RT groups. Cox regression analysis evaluated OS after SPC.

Among 26,254 patients with PC, 20.3% and 79.7% were treated with RT and RP, respectively. Patients with PC had a 7% lower risk of all SPCs than the general male population [standardized incidence ratio (SIR) = 0.93]. Bladder (SIR = 1.65) and thyroid (SIR = 2.75) cancers were more common in both treatment groups. At 10-year follow-up, patients who underwent RP were less likely to have colon cancer than those who underwent RT [risk difference (%) = -0.9]. The former had a lower risk of death following lung (aHRs: 0.70; P = 0.010) and colon (aHRs: 0.53; P = 0.001) SPCs and a higher risk of death following esophageal SPC (aHRs: 6.9; P = 0.008).

SPC incidence and OS after SPC diagnosis may be influenced by the initial PC treatment. The choice of primary treatment for PC should guide the follow-up care and subsequent treatment strategies for SPCs.