M. Miles Braun

Effect of twinship on incidence of cancer of the testis, breast, and other sites (Sweden).

It has been suggested that cancers of the testis and breast are associated with exposure to estrogens and other hormones in utero. Twin pregnancies have higher levels of pregnancy-associated hormones than singleton pregnancies, and these levels may be higher in dizygotic than in monozygotic twin pregnancies. Through a large population-based study of twins, we assessed the hypothesis that levels of pregnancy-associated hormones have etiologic importance for cancers of the testis, breast, and other sites. The incidence of all cancers among 46,767 members of the Swedish Twin Registry was compared with the incidence among the Swedish general population. We found testicular cancer excess among dizygotic twins (observed/expected [O/E] ratio=1.6, 95 percent confidence interval [CI]=1.0–2.6) that was greater for men younger than 35 years (O/E ratio=2.3, CI=1.1–4.2) compared with older men (O/E ratio = 1.2, CI=0.5–2.4). In addition, a substantially elevated incidence of breast cancer was observed in dizygotic twin women aged 20 to 29 years (O/E=6.7, CI=2.9–13.1). None of the other age or zygosity groups showed notable elevations in incidence of testicular, breast, or other cancers. We conclude that dizygotic twinship may be associated with cancer of the breast and testis among young adults. These findings support the concept that pregnancy hormones are associated with risk of testicular and breast cancer, although non-hormonal aspects of twin pregnancy that vary with respect to zygosity cannot be excluded as explanatory factors.

Genetic component of lung cancer: cohort study of twins

Epidemiological and molecular epidemiological findings suggest that inherited predisposition may be a component of lung cancer risk and an important modulator of the carcinogenic effects of cigarette smoke. We have carried out a genetic analysis of lung cancer mortality on the National Academy of Sciences/National Research Council Twin Registry. The registry is composed of 15,924 male twin pairs who were born in the USA between 1917 and 1927 and who served in the armed forces during World War II. As evidence for a genetic effect on lung cancer, we required concordance for lung cancer death to be greater among monozygotic than among dizygotic twin pairs. No genetic effect on lung cancer mortality was observed. The ratio of observed to expected concordance among monozygotic twins did not exceed that among dizygotic twins (overall rate ratio 0.75 [95% CI 0.35-1.6]), even though monozygotic twin pairs are more likely to be concordant for smoking than dizygotic twin pairs in this population. A cohort analysis (accounting for age, sex, race, and smoking intensity) of lung cancer mortality found no lung cancer deaths during 300 person-years of follow-up (observed to expected ratio 0 [0-4.09]) among 47 monozygotic twin smokers whose smoking twins had died of lung cancer, even though smoking histories were very similar within twin pairs. In our study, there is little if any effect of inherited predisposition on development of lung cancer. Genetic factors are not likely to be strongly predictive of lung cancer risk in most male smokers older than 50, the age group in which the vast majority of cases occur.

Infectious complications of biologic treatments of rheumatoid arthritis

&NA; Agents that block the action of tumor necrosis factor‐&agr; and recombinant interleukin‐1 have been shown to be effective biologic treatment modalities in patients with rheumatoid arthritis. Given the immunosuppressive effects of tumor necrosis factor‐&agr; and interleukin‐1 blockers, infections have emerged as possible complications of using these agents, an observation foreshadowed in prelicensure animal studies. At this time, hundreds of thousands of patients have received these drugs, and a wide variety of infectious complications has been reported, among which reactivation tuberculosis is most notable. Case reports alone, however, do not necessarily reflect a causal association between a therapeutic product and an adverse event. The authors review the infectious complications of the use of these agents as reported in the medical literature from November 2001 through October 2002.

Prevalence of a history of testicular cancer in a cohort of elderly twins.

Prior studies have suggested that the risk of testicular cancer among dizygotic twins may exceed that among monozygotic twins or the general population. Cryptorchidism is associated with testicular cancer and twinship, and therefore might potentially explain the findings of the prior studies. In 1993-1994, when they were 66 to 77 years of age, 14,326 twin individuals in the National Academy of Sciences-National Research Council Twin Registry were interviewed by telephone. A history of testicular cancer was reported by 5 (0.08%) of 5951 monozygotic twins and 11 (0.16%) of 6992 dizygotic twins. Follow-up interviews concerning testicular cancer risk factors and treatment were able to be administered to 4 of the monozygotic and 9 of the dizygotic twins reporting testicular cancer. A history of cryptorchidism was reported in the follow-up interview by only one dizygotic twin. Our data agree with the results of prior studies reporting a more frequent occurrence of testicular cancer among dizygotic than monozygotic twins. Although somewhat limited by small numbers, our study also suggests that the findings of increased testicular cancer in dizygotic twins are not explained simply by increased occurrence of cryptorchidism in twins.