Study: Cancer a more potent killer of males
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Sex is known to be a critical factor in the pathogenesis and prognosis of a large number of diseases. “Cancer is a stark example of such—the risk of malignancy is much higher in males, relative to females, for a majority of cancers at most ages,” explained Michael B. Cook, PhD, and co-authors from the division of cancer epidemiology and genetics, at the National Cancer Institute in Bethesda, Md.
Despite these known disparities, no study has explicitly evaluated sex differences in cancer mortality and survival, according to Cook and co-authors. They examined cancer mortality rates among men and women and attempted to partially disentangle the causes of mortality disparities: Are different incidence rates or variability in survival between men and women the chief sources of sex discrepancies in cancer mortality?
Data were pulled from the Surveillance, Epidemiology and End Results (SEER) database for 36 cancers, with trends considered for the period between 1977 and 2006.
Men faced higher age-adjusted mortality rates for all but three cancers: peritoneum, omentum and mesentery; gall bladder; and anus, anal canal and anorectum. For cancers of the lip, larynx, hypopharynx and esophagus, men had between a 4.08 and 5.37 higher risk of mortality than women.
Other marked disparities in cancer rates included urinary bladder, tonsil, oropharynx, floor of mouth and tongue, for all of which men faced mortality rates at least 2.5 times higher than those of women. Men also faced more than double the risk of mortality from cancers of the lung and bronchus, liver and intrahepatic bile duct, and kidney and renal pelvis.
When adjusted for age, stage and grade, men likewise fared worse than women in five-year survival, with markedly higher hazard ratios of death for cancers including skin (minus basal and squamous), endocrine, floor of mouth and lung and bronchus. Men faced lower risks of cause-specific mortality for cancers of the urinary bladder and tongue.
“[T]his analysis shows that male cancer mortality rates were higher than equivalent female rates for a majority of cancers and these differences largely mirror sex differences in cancer incidence. This analysis also shows modestly, but appreciably, worse survival in men for a number of cancers,” wrote Cook and colleagues.
The authors did observe that cancer-specific mortality rates for lung and bronchus, larynx and pancreatic cancers converged somewhat over the last 30 years, before which men faced markedly higher risks of death. In contrast, the risk of mortality for men has increased for cancers of the esophagus, skin (excluding basal and squamous) and liver and intrahepatic bile duct.
“Disparities of cancer mortality have largely paralleled those of cancer incidence…” explained Cook and co-authors. “This supports the idea that sex disparities in cancer mortality arise from the sex differences in cancer incidence.”
Cook and colleagues also pointed to overdiagnosis via screening and detection of asymptomatic cancers as a possible cause of sex-specific differences in cancer survival. They contended that the higher frequency with which females present with less advanced cancers supports this hypothesis, and may suggest that women benefit from broader access, or are more likley to use, available care.
In addition, the authors pointed to several studies that have shown higher comorbidity rates among males, which could likewise skew cancer survival rates in favor of females. Both propositions require further investigation, the authors noted.
“Future analytic studies should focus upon the etiologic factors responsible for the systematically higher cancer incidence rates among men,” Cook and colleagues concluded.