Vitamine D en borstkanker*
Steeds meer wetenschappelijk onderzoek toont het belang aan van goede bloedwaarden
vitamine D tegen het ontstaan en als behandeling bij
borstkanker. Volgens een Canadese deskundige op dit gebied, Professor Pamela Goodwin is mechanisme hoe vitamine D in het lichaam tegen kanker werkt al redelijk duidelijk. Eigenlijk zou er meer onderzoek moeten komen naar de juiste dosering om goede bloedwaarden vitamine D te krijgen en te handhaven.
Vitamin D in Breast Cancer -- the Debate Continues: An Expert Interview With Dr. Pamela J. Goodwin
Editor's Note: Evidence is accumulating that suggests a link between low vitamin D levels and poor prognosis in breast cancer. However, while studies demonstrate an association between the two, clinicians are faced with the task of addressing the issue with patients and answering questions about vitamin D supplementation. Selecting an optimal dose for supplementation can be especially challenging because little correlation exists between the amount of vitamin D consumed and blood levels. At the 2009 Annual Meeting of the American Society of Clinical Oncology, held in Orlando, Florida, from May 29 to June 2, 2009, additional studies regarding vitamin D and breast cancer were presented. While at the ASCO meeting, Medscape Oncology contributor Emma Hitt, PhD, discussed the role of vitamin D in breast cancer and recent findings on the topic with Pamela J. Goodwin, MD, a Senior Investigator at the Samuel Lunenfeld Research Institute of Mount Sinai Hospital, in Toronto, Ontario, Canada.
Medscape: You recently reported the findings of a prospective study in the Journal of Clinical Oncology showing that low vitamin D levels were associated with poor outcomes in breast cancer. Can you describe those findings and their clinical significance?
Dr. Goodwin: We evaluated a cohort of 512 women who had been diagnosed with breast cancer between 1989 and 1996, and at the time of diagnosis, we measured their vitamin D levels -- after surgery but before they started treatment.[1] We then followed them for 11.6 years; during that time, 116 women had distant recurrences, and 106 women died. We found that women with low vitamin D levels tended to be more obese and to have higher-grade tumors.
They were also at a greater risk for both distant recurrence and death; low levels of vitamin D were associated with an increased risk for distant recurrence, with a hazard ratio of 1.94 (ie, an almost doubled risk). Decreased survival was also associated with the lowest vitamin D levels, with a hazard ratio of 1.73. For the most part, these effects remained significant upon multivariate analyses, even after adjusting for a large number of factors.
What we found, though, was an association, not a cause-and-effect relationship (ie, we are unable to say that the low vitamin D caused the poor outcomes). Vitamin D levels are associated with a large number of factors, including diet, physical activity, sun exposure, and general overall health. Although we tried to control for as many of those as we could, in this observational setting it could not be definitively concluded that these outcomes resulted from low levels of vitamin D.
Medscape: What are the potential mechanisms that may explain this association?
Dr. Goodwin: We measured 25-hydroxy vitamin D, the predominant circulating form of vitamin D in the blood, which is converted in breast cancer tissue to the active form, 1,25-dihydroxy vitamin D. This then binds to vitamin D receptors present on breast cancer cells, and the vitamin D receptors then translocate to the nucleus, bind to vitamin D response elements in genes, and regulate the transcription of over 200 genes that are responsible for proliferation, differentiation, apoptosis, and adhesion; thus, the biology for an effect of vitamin D in breast cancer is quite strong. Several studies at ASCO this year addressed the association between vitamin D and breast cancer.
Medscape: What were some of the findings presented with respect to this topic?
Dr. Goodwin: One study was an analysis of postmenopausal breast cancer patients from the NCIC-CTG MA14 trial,[2] evaluating serum 25-hydroxy vitamin D levels and prognosis; this study found no association between vitamin levels and event-free survival or relapse-free survival. Vitamin D levels were measured and available in 607 patients in the phase 3 MA.14 trial, which evaluated adjuvant tamoxifen with or without octreotide (90 mg/month depot injection for 2 years). Dr. Piura and colleagues had hypothesized that baseline serum D might be associated with relapse of breast cancer in bone and/or other metastatic sites, but no such association was found.
Another study evaluated the relationship between vitamin D levels and obesity,[3] which has been the subject of many studies with contrasting results. For instance, guidelines for vitamin D intake do not take body mass index (BMI) into consideration. The researchers examined the relationship between serum 25-hydroxy vitamin D and BMI in 740 cancer patients presenting at the Cancer Treatment Centers of America between January and June 2008. The mean BMI was 27.9 kg/m2 (standard deviation [SD] = 6.7). Of those patients, 18% had lung cancer, 13% had colorectal cancer, 11.6% had pancreatic cancer, 6% had prostate cancer, and 5% had ovarian cancer. They found that as BMI level increased from normal weight to overweight to obese, vitamin D decreased significantly (P = .001). For each 1-kg/m2 increase in BMI, there was a mean decline of 0.43 ng/mL in serum vitamin D (P = .001).
Another study by the same research group evaluated serum 25-hydroxy vitamin D and nutritional status in the same cohort of patients.[4] Trukova and colleagues hypothesized that mean serum 25-hydroxy vitamin D levels may be significantly lower in malnourished oncology patients compared with patients with adequate nutritional status. They assessed nutritional status using Subjective Global Assessment, which classifies patients according to 3 levels of nutritional status, and serum albumin, divided into 2 groups: ≥ 3.6 g/dL and < 3.6 g/dL. Mean serum albumin and serum vitamin D were 3.5 g/dL (SD = 0.6) and 21.9 ng/mL (SD = 13.5), respectively. Vitamin D levels were low across the cohort, and no significant difference in the mean vitamin D levels across serum albumin or across the 3 categories of nutritional status was noted. Thus, vitamin D deficiency was found to be prevalent among cancer patients regardless of nutritional status, suggesting that screening for vitamin D deficiency and vitamin D repletion should be considered for all cancer patients.
In a study conducted at the Cleveland Clinic[5] that measured prevalence and risk factors for vitamin D insufficiency in cancer, researchers found that vitamin D insufficiency was common among the cancer patients tested. They reviewed electronic medical records of all adult solid tumor patients (n = 39,254) treated from 2006 to 2007. Of those, 2100 patients had vitamin D levels evaluated. The patients tested were more likely to be female (66% vs 47%) and to have breast, hepatobiliary, skin, or thyroid cancer than those not tested (P < .001, for both). Of the patients tested, 69% had insufficient vitamin D levels, and 10% had a frank deficiency of < 12 ng/mL. Upon multivariate analysis, insufficiency was associated with male gender, African American race, and month of test (February, March, April, and October). Low levels were also found more often in patients with low albumin and in those not receiving antineoplastic medication or vitamin D supplementation (P < .01 for all).
In another study,[6] Khan and coworkers, from the University of Kansas Medical Center, evaluated the effect of high-dose vitamin D supplementation (50,000 IU/wk) on 25-hydroxy vitamin D levels in postmenopausal breast cancer patients with baseline levels below 40 ng/mL who were starting on an aromatase inhibitor. After 6 weeks of supplementation, 98% of the patients achieved levels higher than 40 ng/mL; however, after 12 weeks, when vitamin D supplementation was reduced to 600 to 1000 IU per day, levels fell by 6.8% per month over the subsequent 3 to 6 months. The investigators concluded that standard doses of 600 to 1000 IU per day were inadequate to maintain high vitamin D levels.
References
1. Goodwin PJ, Ennis M, Pritchard KI, Koo J, Hood N. Prognostic effects of 25-hydroxyvitamin D Levels in early breast cancer. J Clin Oncol. 2009 May 18. [Epub ahead of print]
2. Piura E, Chapman JW, Lipton A, et al. Serum 1-OH vitamin D (D) and prognosis of postmenopausal breast cancer (BC) patients: NCIC-CTG MA14 trial. J Clin Oncol. 2009;27(15 suppl):Abstract 534.
3. Gupta D, Trukova K, Vashi PG, et al. Association of serum 25-hydroxy vitamin D and body mass index in cancer. J Clin Oncol. 2009;27(15 suppl):Abstract 6625.
4. Trukova K, Gupta D, Vashi PG, et al. Serum 25-hydroxy vitamin D and nutritional status: Implications for vitamin D assessment and dietary supplementation in oncology. J Clin Oncol. 2009;27(15 suppl):Abstract 9638.
5. Hauser KA, Karafa M, Seyidova-Khoshknabi D, Davis MP, Walsh D. Prevalence and risk factors of vitamin D insufficiency in cancer. J Clin Oncol. 2009;27(15 suppl):Abstract 9581.
6. Khan QJ, Kimler BF, Sharma P, et al. Vitamin D levels during and after high-dose vitamin D supplementation in women with early-stage breast cancer. J Clin Oncol. 2009;27(15
suppl):Abstract e20561.
(Juli
2009)
