The source is neither from soy manufacturers or anti-soy groups.  I got the article from MescapeCME which is a continuing ed source for nurses, and you have to register, so I can't link it.  The study was published in the Journal of the American Medical Association which charges for their articles. 

But the bottom line of this study (mind you, it's one study, but a legit one) is:  "Among women with breast cancer, soy food consumption was significantly associated with decreased risk of death and recurrence," the study authors write."

December 14, 2009 — Dietary soy intake among Chinese women with breast cancer is significantly associated with lower risk for death and recurrence, according to the results of a large, population-based cohort study reported in the December 9 issue of the Journal of the American Medical Association.

"Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer," write Xiao Ou Shu, MD, PhD, from Vanderbilt University Medical Center in Nashville, Tennessee, and colleagues. "However, the estrogen-like effect of isoflavones and the potential interaction between isoflavones and tamoxifen have led to concern about soy food consumption among breast cancer patients."

The study goal was to determine the association of dietary soy intake after diagnosis of breast cancer with total mortality and cancer recurrence. In the Shanghai Breast Cancer Survival Study of 5042 female breast cancer survivors in China, women 20 to 75 years of age who were diagnosed between March 2002 and April 2006 were recruited and followed up through June 2009.

At about 6 months after cancer diagnosis, participants provided information on cancer diagnosis and treatment, lifestyle exposures after cancer diagnosis, and disease progression. Three follow-up interviews at 18, 36, and 60 months after diagnosis allowed updating of this information. To obtain survival information for participants who were lost to follow-up, the investigators used annual record linkage with the Shanghai Vital Statistics Registry database. Disease and treatment information were verified from medical record review.

Primary study endpoints were total mortality and breast cancer recurrence or breast cancer–related deaths. Adjustment for known clinical predictors and other lifestyle factors was performed using Cox regression analysis, with dietary soy intake treated as a time-dependent variable. Median follow-up was 3.9 years (range, 0.5 - 6.2 years).

During follow-up of 5033 breast cancer patients treated with surgery, there were 444 deaths and 534 recurrences or breast cancer–related deaths. Soy food intake, measured by either soy protein or soy isoflavone intake, was inversely associated with mortality and recurrence. Compared with the lowest quartile of intake of soy protein intake, the hazard ratio for the highest quartile was 0.71 (95% confidence interval , 0.54 - 0.92) for total mortality and 0.68 (95% CI, 0.54 - 0.87) for recurrence. For women in the lowest and highest quartiles of soy protein intake, the multivariate-adjusted 4-year mortality rates were 10.3% and 7.4%, and the 4-year recurrence rates were 11.2% and 8.0%, respectively. Women with either estrogen receptor–positive or estrogen receptor–negative breast cancer exhibited this inverse association, as did both users and nonusers of tamoxifen.

"Among women with breast cancer, soy food consumption was significantly associated with decreased risk of death and recurrence," the study authors write.

Limitations of this study include a relatively short follow-up period and limited statistical power for subanalyses, such as estrogen receptor status or tamoxifen use status.

"In this population-based prospective study, we found that soy food intake is safe and was associated with lower mortality and recurrence among breast cancer patients," the study authors conclude. "The association of soy food intake with mortality and recurrence appears to follow a linear dose-response pattern until soy food intake reached 11 grams/day of soy protein; no additional benefits on mortality and recurrence were observed with higher intakes of soy food. This study suggests that moderate soy food intake is safe and potentially beneficial for women with breast cancer."

In an accompanying editorial, Rachel Ballard-Barbash, MD, MPH, from the National Cancer Institute in Bethesda, Maryland, and Marian L. Neuhouser, PhD, from the Fred Hutchinson Cancer Research Center in Seattle, Washington, note differences between China and the United States in the quality, type, and quantity of soy food intake. Differences in screening rates and other factors in China compared with the United States may also preclude comparisons of stage- and treatment-specific results.

"Even though the findings by Shu et al suggest that consumption of soy foods among breast cancer patients is probably safe, studies in larger cohorts are required to understand the effects of these foods among diverse clinical subgroups of breast cancer patients and survivors," the editorialists write. "In the meantime, clinicians can advise their patients with breast cancer that soy foods are safe to eat and that these foods may offer some protective benefit for long-term health. Moreover, the potential benefits are confined to soy foods, and inferences should not be made about the risks or benefits of soy-containing dietary supplements."

The US Department of Defense Breast Cancer Research Program and the National Cancer Institute supported this study. Dr. Shu reports having received a research development fund from the United Soybean Board in 2005. The other study authors and editorialists have disclosed no relevant financial relationships.

JAMA. 2009;302:2437-2443, 2483-2484.

Clinical Context

Adjuvant therapy for breast cancer includes blocking the effect of estrogen, noted by Moundsen and colleagues in the August 2003 issue of Breast. Isoflavones, a major group of phytoestrogens found in soy foods, have estrogen-like and antiestrogenic effects, as reported by Adlercreutz and Mazur in the April 1997 issue of the Annals of Medicine. In the April 5, 2006, issue of the Journal of the National Cancer Institute, a meta-analysis by Trock and colleagues found an inverse relationship between soy food intake and the risk for breast cancer. However, it is not clear whether breast cancer treatment and soy isoflavones might interact in an adverse manner.

This longitudinal, population-based cohort study, using the Shanghai Breast Cancer Survival Study data, assesses the link between soy food intake and mortality and breast cancer recurrence in women diagnosed with breast cancer.

Study Highlights

•5042 women aged 20 to 75 years were recruited into the Shanghai Breast Cancer Survival Study during a 4-year period approximately 6 months after breast cancer diagnosis.
•Exclusion criteria were refusal to participate, absence during enrollment, lack of contact, and health or communication problems.
•Nonparticipants vs participants were similar in age but were more likely to have advanced stage of cancer.
•The investigators conducted data analysis on 5033 patients, after excluding 9 patients who did not have surgical treatment.
•Data on cancer diagnosis, treatment, lifestyle exposures after diagnosis, and disease progression were obtained approximately 6.5 months after diagnosis.
•3 follow-up interviews are scheduled at 18, 36, and 60 months after diagnosis.
•Soy intake was measured by a validated food frequency questionnaire at 18 months for the prior 12 months and at 36 months for the preceding 18 months.
•Soy intake was categorized by quartile: first (≤ 5.31 g/day of soy protein or ≤ 20 mg/day of isoflavones), second (5.32 - 9.45 g/day of soy protein or 20.01 - 36.50 mg/day of isoflavones), third (9.46 - 15.31 g/day of soy protein or 36.51 - 62.68 mg/day of isoflavones), and fourth (> 15.31 g/day of soy protein or > 62.68 mg/day of isoflavones).
•4354 (88.2%) of 4934 patients completed the 36-month interview at time of study publication.
•1868 patients completed the 60-month interview, which is ongoing.
•Disease and treatment data were confirmed by review of medical charts and pathologic slides.
•Survival information for patients lost to follow-up was obtained from the Shanghai Vital Statistics Registry.
•The main outcome measures were total mortality and recurrence rates (breast cancer recurrence or breast-cancer related death).
•Analysis adjusted for age at diagnosis, TNM stage, chemotherapy, radiotherapy, type of surgery, body mass index, menopause status, estrogen and progesterone receptor status, tamoxifen use, educational level, income, cruciferous vegetable intake, total meat intake, vitamin supplement use, tea intake, and physical activity.
•Median follow-up was 3.9 years (range, 0.5 - 6.2 years).
•444 deaths occurred.
•534 breast cancer recurrences or breast cancer-related deaths occurred.
•Highest vs lowest quartile of soy protein intake was linked with lower mortality rates (hazard ratio, 0.71; 95% CI, 0.54 - 0.92).
•Adjusted 4-year mortality rates were greater for lowest vs highest quartiles of soy protein intake (10.3% vs 7.4%).
•Highest vs lowest quartile of soy protein intake was linked with lower breast cancer recurrence (hazard ratio, 0.68; 95% CI, 0.54 - 0.87).
•Adjusted 4-year breast cancer recurrence rates were greater for lowest vs highest quartiles of soy protein intake (11.2% vs 8.0%).
•The link between soy protein or isoflavone intake and mortality and recurrence followed a linear dose-response pattern until soy protein intake reached 11 g/day or soy isoflavone intake reached 40 mg/day.
•The associations of soy intake with mortality and breast cancer recurrence were similar in estrogen receptor–positive or estrogen receptor–negative breast cancer and with or without tamoxifen use.
•Study limitations included relatively short follow-up period and limited power for subanalysis of estrogen receptor and tamoxifen use.

Clinical Implications

•In women with breast cancer, higher intake of soy food is linked with a decreased risk for mortality.
•In women with breast cancer, higher intake of soy food is linked with a decreased risk for breast cancer recurrence.

CME/