Potent Social Forces Influence Smoking Behavior
In 1971, the places smokers and nonsmokers held in the social network were indistinguishable. But three decades later, societal views of smoking have changed, and smokers are increasingly at the periphery of social networks and aligned largely with other smokers, according to results published in the May 22 New England Journal of Medicine.
The authors, Drs. Nicholas Christakis of Harvard Medical School and James Fowler of the University of California, San Diego, reported last year that social networks may strongly influence obesity. In the current study, the authors demonstrate that decisions to quit smoking often reflect changes made by groups of people connected to each other, both directly and indirectly. For example, when a spouse quit smoking, the partner's chances of smoking decreased by 67 percent; friends who quit smoking decreased one another's chance of smoking by 36 percent.
The network phenomenon could potentially be exploited to spread positive health behavior, the study concludes. Along these lines, collective interventions may be more effective than individual interventions, and public health strategies to encourage smoking cessation may be more cost-effective than initially thought, since health improvements in one person may well spread to others.
MRI May Contribute to Rising Mastectomy Rates
The number of mastectomies performed at the Mayo Clinic in Minnesota for women with early stage breast cancer jumped by 13 percent between 2003 and 2006, rising from 30 percent to 43 percent. A new study suggests that the introduction of preoperative breast magnetic resonance imaging (MRI), which is more sensitive than traditional mammography, may have been a factor.
An analysis of more than 5,400 women with early stage breast cancer who had surgery at the Mayo Clinic between 1997 and 2006 showed that women who received preoperative MRI were significantly more likely to undergo mastectomy than those who did not, though mastectomy rates rose in both groups. Co-author Dr. Matthew P. Goetz recently briefed the media on the findings, which will be presented next month at the American Society of Clinical Oncology annual meeting.
Preoperative breast MRI can detect cancer in more than one part of the breast, and this may lead physicians and patients to choose mastectomy over lumpectomy. About half of the lesions detected by MRI are not cancerous and only need to be monitored, but some women with these lesions may still choose mastectomy for various reasons, according to the researchers.
Mastectomy rates declined from 45 percent in 1997 to 30 percent in 2003, but then rose to 43 percent in 2006, the study found. During this period, the percentage of women who had breast MRI doubled to 22 percent. Half of the patients receiving MRI underwent mastectomy, compared with 38 percent of women who did not have MRI. Mastectomy rates also rose in women who did not have preoperative MRI (from 28 percent in 2003 to 41 percent in 2006).
Dr. Julie Gralow of the University of Washington, who moderated the briefing, cautioned that more research is needed to determine whether the additional surgeries improve outcomes and increase overall survival. A recent study showing an increase in preventive double mastectomies has similarly raised questions about the risks and benefits of these surgeries.
BRCA2 Linked to Prostate Cancer Incidence and Aggression
A study by researchers in Australia and Canada shows that BRCA2 mutation-positive men from BRCA mutation-positive families are at 3.5 times the risk of developing prostate cancer, and at higher risk of aggressive prostate cancer, compared with the general population. No increase in prostate cancer risk was observed in BRCA1 mutation-positive men in this study. The report appeared in the May 15 issue of Clinical Cancer Research.
The researchers examined 137 families that were known to have germline BRCA1 or BRCA2 mutations and that also had at least one male member who was diagnosed with prostate cancer. Among these families, 158 such men were candidates for the study. Lack of available prostate biopsies limited the analysis to 18 prostate cancer patients, 4 of whom carried germline BRCA1 mutations and 14 with germline BRCA2 mutations.
Loss of heterozygosity - in which one copy of a defective gene is inherited and the other copy becomes defective some time after birth, perhaps due to environmental factors - was detected in the prostate tumor tissue from 10 of the 14 BRCA2 carriers. The men whose cancers displayed loss of heterozygosity had exceptionally high Gleason scores of 7 to 9 (the median score was 9), and they had stage II or higher cancers.
"Although the sample size is small," the authors wrote, "these results indicate that BRCA2 has the hallmarks of a tumor suppressor and is the likely cause of the prostate cancer in a substantial portion of carriers who are diagnosed with the disease." The data add to prior information suggesting that prostate cancer may be part of the hereditary breast/ovarian cancer syndrome. The researchers added that there are no data to support a mechanism by which BRCA2 may cause prostate cancer.
The authors noted that BRCA2 mutation-positive (but not BRCA1 mutation-positive) men from hereditary breast/ovarian cancer families should be considered at significantly increased risk of prostate cancer by clinicians responsible for their care. They also suggest that additional evidence is required to formulate the specific screening advice and optimal management recommendations required to reduce the burden of prostate cancer in genetically at-risk men.
Vitamin D Not Associated with Decreased Prostate Cancer Risk
In a nested case-control study of participants from the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial, published online May 27 in the Journal of the National Cancer Institute, higher concentrations of serum 25-hydroxy vitamin D [25(OH)D], the primary form of vitamin D circulating in the bloodstream, were not associated with a decreased risk of prostate cancer. In fact, concentrations greater than the lowest fifth of the spectrum tended to be associated with an increased risk of aggressive disease.
Researchers in NCI's Division of Cancer Epidemiology and Genetics collected data on serum 25(OH)D concentrations from 749 white men diagnosed with prostate cancer and 781 controls, from samples taken at the beginning of their participation in the PLCO study (at baseline). All participants were taken from the PLCO trial screening arm, which includes annual standardized prostate cancer screening.
Serum 25(OH)D concentration was not associated with risk for prostate cancer overall, nor with non-aggressive disease; however, the researchers did see some evidence of an increased risk of aggressive disease associated with higher concentrations of vitamin D. They note that in their analyses not all the trends were statistically significant nor did the associations generally show a linear dose-dependence.
"In summary, results from this large prospective study of men who underwent standardized prostate cancer screening in the context of a screening trial do not support the hypothesis that higher serum vitamin D status is associated with decreased risk of prostate cancer," state the authors in an accompanying press release. "It raises the possibility that higher vitamin D level may be associated with increased risks for aggressive disease, [but] a clear monotonic dose-response relationship was lacking."