We carried out a cohort study in the Italian province of Trieste (2001 population, 242,000) to ascertain whether the risk of a subsequent primary cancer among 265 individuals diagnosed with a first malignancy at ages up to 25 years between 1971 and 1993 differed from that in the general population and to evaluate the effect of cancer family history, quantified by the family risk index (FRI), on the occurrence of second primaries. During the follow-up (median duration = 10 years; 25th-75th percentile = 2-16), 15 cohort members developed a second cancer vs. 1.60 expected for a standardized incidence ratio (SIR) of 9.4 (p < 0.0001). The overall SIR fell to 4.7 (p = 0.004) after excluding the 8 patients with well-known cancer-predisposing conditions (SIR = 300.0; p < 0.0001) and the 50 with a positive family history (FRI &GE; 1.0) of malignant tumors (SIR = 20.0; p < 0.0001). Among 114 patients treated with radiotherapy and chemotherapy for their first neoplasms and not affected by predisposing disorders, 23 with a positive family history of cancer showed a 6.4-fold excess risk of second primaries (p = 0.008) compared with 91 with a negative history (FRI < 1.0). It is imperative that clinicians carefully and regularly evaluate cancer family history of young patients with malignancies. This would enable them to identify possible individual and familial features in patients at higher risk of multiple primaries and to adopt more suitable preventive and therapeutic measures
