Nevertheless, the established risk factors for prostate cancer continue to be older age, black race, family history, and genetic aberrations, such as BRCA mutations.
But a new study has added urgency to the question of whether or not baldness is also a risk factor.
For the first time, researchers have found that baldness is tied to the risk for prostate cancer death.
In fact, the risk is 1.5 times greater in bald men than in those with no baldness, according to an analysis of data from the large American prospective, longitudinal cohort study known as the National Health and Nutrition Examination Survey Epidemiologic Follow-up Study (NHEFS).
The results were published in the February 1 issue of the American Journal of Epidemiology.
NHEFS is a "unique resource," Michael Cook, PhD, an epidemiologist in the division of cancer epidemiology and genetics at the National Cancer Institute (NCI) in Bethesda, Maryland, and his colleagues report.
They explain that, of the various datasets used to show associations between baldness and prostate cancer, NHEFS is distinctive because it now has — for the first time ever — a long enough median follow-up (21 years) to assess death risk. It also has a "major advantage" because participants were dermatologically assessed for baldness at baseline.
The researchers looked at data on 4316 men in the NHEFS cohort who, at baseline (1971 to 1974), were 25 to 74 years of age and had no previous cancer diagnosis.
To date, there have been 3284 deaths in the cohort, 107 of which were caused by prostate cancer.
In multivariable models, the risk for fatal prostate cancer was 56% higher in men with any baldness than in those with no baldness (hazard ratio [HR], 1.56; 95% confidence interval [CI], 1.02 - 2.37). In men with moderate balding, specifically, the risk was 83% higher (HR, 1.83; 95% CI, 1.15 - 2.92).
Despite the findings, baldness is not a certain risk factor for prostate cancer, Dr Cook said.
However, "it is conceivable that, in the future, patterns and degree of male baldness may play a small role in estimating risk of prostate cancer," he told Medscape Medical News in an email.
An urologist not involved with the study echoed these comments.
"The 50% higher risk of disease-specific mortality is important but modest," said Stephen Freedland, MD, from the Cedars-Sinai Samuel Oschin Comprehensive Cancer Institute in Los Angeles.
He provided some context: other studies have shown that the risk is about 2.5 times higher in black men than in white men.
Furthermore, the risk elevation associated with baldness is especially modest compared with, for example, the increased risk for lung cancer death associated with smoking, he told Medscape Medical News.
Dr Freedland knows this subject well. In 2013, he and colleagues conducted a case–control study at a Veterans Affairs hospital of 708 men with and without prostate cancer (Cancer Causes Control. 2013;24:1045-1052). They found that overall balding was associated with more than a twofold increase in high-grade disease (P = .02).
Those findings are akin to another study conducted by Dr Cook's team, which showed an association between baldness and aggressive prostate cancer in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, as reported by Medscape Medical News.
"We found the same thing," Dr Freedland reported.
Should Baldness Be Designated a Risk?
Overall, epidemiologic evidence of the link between baldness and prostate cancer is largely consistent, showing a modest association, both Dr Cook and Dr Freedland acknowledged.
But Dr Freedland was a bit bolder in his interpretation of the data. "The moral of the story is that bald men have a higher risk of prostate cancer," he said.
So, should baldness be included as a risk factor for prostate cancer, even if it is just as a modest one?
Not yet, said Dr Cook. "Replication of our results is required, as is a better mechanistic understanding of this association," he explained.
"It's not far off from prime time, but not there yet," Dr Freedland added.
This will be news to many urologists, he continued, because they don't tend to read epidemiology journals, where all of the baldness and prostate cancer studies have been published. "Urologists in the United States read the Journal of Urology," he asserted.
"Observations from epidemiology eventually migrate to the clinical world," he explained, noting that even obvious cancer risk factors, such as smoking for lung cancer, started off as rarified epidemiologic findings.
What matters now, said Dr Freedland, is that research that seeks to elucidate the implications of baldness, as it relates to prostate biology, be funded. "We need to know about androgen levels in the prostates of bald men," he said.
There are other areas of this research that need to be explored further, including the relation between prostate cancer and distinct patterns of baldness, as well as age at the onset of baldness, Dr Cook and his colleagues note.
Data on specific hair-loss scalp patterns in the NHEFS cohort are limited. Baseline baldness was assessed by trained third-year dermatology residents using a procedure that was standard in the 1970s.
Baldness was categorized into four levels, but there was no differentiation between the bitemporal, frontal, and vertex areas. It is the vertex area that is now thought to especially increase the likelihood of prostate cancer. Male pattern baldness was, however, differentiated from other causes, such as trauma and alopecia areata, in the NEHFS cohort.
The study authors and Dr Freedland have disclosed no relevant financial relationships.
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Linked: Baldness, Risk for Prostate Cancer Death. Medscape. Feb 10, 2016.