Muscular dystrophy patients appear more prone to some cancers

Patients with myotonic muscular dystrophy were at increased risk of cancer, both overall and specifically from malignancies of the endometrium, brain, ovary and colon, according to a Scandinavian registry study.

Researchers identified 1,658 patients with a muscular dystrophy discharge diagnosis in national Swedish and Danish patient registries between 1977 and 2008, then linked them to their countries' respective cancer registries. Patients were followed from date of first muscular dystrophy diagnosis to first cancer diagnosis, death, emigration or exit from the cancer registry. Results appeared in the Dec. 14 Journal of the American Medical Association.

In the study, 104 patients with muscular dystrophy developed cancer, or 73.4 per 10,000 person-years with muscular dystrophy compared to an expected rate of 36.9 per 10,000 person-years in the general Swedish and Danish populations combined (standardized incidence ratio [SIR], 2.0; 95% CI, 1.6 to 2.4).

There were significant excess risks of cancer for several organ systems:

• endometrium (n=11; observed rate, 16.1 per 10,000 person-years; SIR, 7.6; 95% CI, 4.0 to 13.2),
• brain (n=7; observed rate, 4.9 per 10,000 person-years; SIR, 5.3; 95% CI, 2.3 to 10.4),
• ovary (n=7; observed rate, 10.3 per 10,000 person-years; SIR, 5.2; 95% CI, 2.3 to 10.2), and
• colon (n=10; observed rate, 7.1 per 10,000 person-years; SIR, 2.9; 95% CI, 1.5 to 5.1).

Cancer risks were similar in women and men after excluding genital organ tumors (SIR, 1.9; 95% CI, 1.4 to 2.5 vs. SIR, 1.8; 95% CI, 1.3 to 2.5, respectively; P=0.81 for heterogeneity; observed rates, 64.5 and 47.7 per 10,000 person-years in women and men, respectively). In age-stratified analyses of patients younger than 50 years old compared to those older than that, no statistically significant difference was observed in overall cancer risk (SIR, 2.2; 95% CI, 1.4 to 3.2 vs. SIR, 1.9; 95% CI, 1.6 to 2.4, respectively; P=0.58 for heterogeneity; observed rates, 25.7 and 165.6 per 10,000 person-years in the younger and older groups, respectively).

There was a significantly higher excess risk of endometrial cancer among women younger than 50 years (n=5; observed rate, 11.1 per 10,000 person-years; SIR, 35.6; 95% CI, 13.0 to 78.9) compared to women 50 years and older (n=6; observed rate, 25.8 per 10,000 person-years; SIR, 4.6; 95% CI, 1.9 to 9.5; P=0.003 for heterogeneity).

Clinical management of myotonic muscular dystrophy patients should include routine population-based cancer screening strategies, particularly for colon cancer, and careful assessment of therapy-related risks and benefits, the authors concluded.

They wrote, “The incidence rates for a number of the excess cancers are relatively low, despite their large relative risks. Screening for these uncommon cancers should not be implemented in the absence of demonstrated clinical utility. The evaluation of persistent central nervous system and abdominopelvic symptoms or dysfunctional uterine bleeding warrants clinical consideration with a higher prior probability of neoplasm, in light of our new findings.”