A recent study published in Clinical Breast Cancer found that vitamin D supplementation taken concurrently with chemotherapy may improve disease-free survival in women with HER2+ breast cancer.
October is Breast Cancer Awareness Month, a time for people to take the proper steps for early detection of the disease and to encourage others to do so, as well. To learn more, visit the National Breast Cancer Foundation’s website.
Among women, breast cancer is the most commonly diagnosed cancer, and the second most common cause of cancer deaths. Epidermal growth factor receptor 2 positive (HER2+) breast cancers account for 20% of newly diagnosed breast cancer cases.
HER2 is a gene that encodes for HER2 receptors. In a healthy person, HER2 receptors help regulate how breast cancer cells grow and divide.
In one fifth of breast cancer patients, HER2 genes do not work properly and make too many copies of themselves, resulting in excessive amounts of HER2 receptors. The overexpression of HER2 receptors cause the breast cells to grow and divide uncontrollably, eventually leading to HER2+ breast cancer.
Healthy breast cells, as well as breast cancer cells, express vitamin D receptors and the enzyme used for the activation of vitamin D. This has led researchers to speculate that vitamin D plays a role in the development and progression of breast cancer.
In support of these speculations, studies have consistently shown a relationship between vitamin D status and breast cancer incidence. However, research has not investigated the relationship between vitamin D and HER2+ breast cancer, specifically.
Recently, researchers performed a retrospective review on 134 patients with non-metastatic HER2+ breast cancer who received vitamin D supplements during chemotherapy and 112 patients with non-metastatic HER2+ breast cancer who did not receive vitamin D supplements during chemotherapy.
The researchers found that most those who were supplementing with vitamin D were receiving on average a low dosage of 10,472 IU/week. Only 33.3% of the patients were vitamin D deficient (as defined by levels less than 20 ng/ml) prior to chemotherapy treatment. The researchers attributed the low incidence of deficiency to the fact that most participants were living in Florida, a location with high UV exposure.
The researchers compared the two groups’ average disease-free survival and the overall survival between 2006-2012.
Disease-free survival refers to the length of time that a HER2+ breast cancer patient survives without any signs or symptoms of HER2+ breast cancer. Whereas, overall survival denotes the length of time that the patient is still alive whether or not they are showing signs or symptoms.
They wanted to see how the use of vitamin D supplements, no matter the dose, influenced these two different measurements of survival.
Here is what they found:
- Patients supplementing with vitamin D had a significantly improved five year disease-free survival compared to the patients who did not supplement with vitamin D, with an average 69.2% and 48.3% survival rates, respectively (p = .022).
- Patients receiving vitamin D had a non-signficant improved overall survival compared to the patients who did not receive vitamin D, with averages 95.4% and 88.9% survival rate, respectively (p = .07).
- Vitamin D supplementation was associated with a 69% lower chance of mortality within 5 years (p = .03)
The researchers adjusted the results for potential confounding factors. The analyses had similar findings:
- Vitamin D supplementation significantly improved disease-free survival compared to those who did not supplement (p = .03).
- There were no significant differences between those that supplemented with vitamin D and those that did not in overall survival.
There were no significant differences between the two groups for any category in overall survival, which included tumor size, number of metastatic lymph nodes, age at diagnosis, or lymphovascular invasion.
The researchers summarized their findings,
“Our study suggests that vitamin D supplementation in patients with non-metastatic HER2+ breast cancer was associated with improved disease free survival, and the relationship remained significant after adjusting for potential confounding factors.”
They went on to add,
“The potential practice-changing significance of our findings and the favorable risk-benefit ratio of vitamin D supplement use warrants a larger prospective trial to further study the impact of vitamin D supplementation in the treatment of HER2+ breast cancer.”
The researchers noted several limitations. Since the vitamin D supplementation was not randomly given to patients, selection bias may have occurred. Patients with a better prognosis may have been more likely to receive vitamin D supplementation or vice versa. In addition, the sample size was rather small, limiting the study’s power.
Clinical trials need to investigate the effects of correcting for vitamin D deficiency in patients with HER2+ breast cancer. Since most of these patients were not vitamin D deficient and were only taking a low dosage of vitamin D, the effects of vitamin D supplementation could have been potentially minimized.