Impact of family history of cancer on risk and mortality of second cancers in patients with prostate cancer.

BACKGROUND: Survival rates are increasing in patients with prostate cancer, and second primary cancers (SPCs) are becoming more common in these patients. However, the etiology and clinical consequences of SPCs are not well-known. We define the impact of family history on SPC and causes of mortality in these patients.

PATIENTS AND METHODS: A nation-wide cohort study based on the Swedish Family-Cancer Database covering 4.4 million men and 80,449 prostate cancers diagnosed between 1990 and 2015. Relative risks (RRs) and cumulative incidence for SPCs and for familial SPC were calculated for prostate cancer patients.

RESULTS: SPC was diagnosed in 6,396 men and more than a third of these patients had a first-degree family history of any cancer; the familial risk was 1.37 (95% CI: 1.27-1.40), compared to 1.10 (1.08-1.16), without a family history. Cumulative incidence by the age of 83 years reached 21% for prostate cancer alone, 28% in those with SPC, and 35% in patients with SPC and family history. Family history was associated with the risk of seven specific SPCs, including colorectal, lung, kidney, bladder and skin (both melanoma and squamous cell) cancers, and leukemia. Colorectal and lung cancers were common SPCs, and family history doubled the risk of these SPCs. In patients with SPC, half of all causes of death were due to SPC and only 12.77% were due to prostate cancer. Most deaths in SPC were caused by lung and colorectal cancers.

CONCLUSIONS: SPCs were an important cause of death in patients with prostate cancer and family history was an important risk factor for SPCs. Prevention of SPC should be essential when prostate cancer survival rates are being improved and this could start by conducting a thorough assessment of family history at the time of prostate cancer diagnosis.