Vitamin D and breast cancer.

Sir,

We read with a great interest Imtiaz et al.'s paper published recently in Indian journal of Endocrinology and metabolism.[1] They skillfully design a study to determine a possible relationship between grade/stage of breast cancer (BC) and serum level of Vitamin D. Finally, they concluded that “almost all patients with breast cancer were vitamin D deficient and tumor characteristics did not show any significant associations with serum levels of vitamin D.” Although this issue is a hot topic in endocrinology and oncology but in this study there are some concerns which undermine the results to make a definite conclusion.

One of the most important queries in this study is amount of cases. We can claim that if the difference between two groups (BC and Healthy) was not significant, it could because of small amount of sample size. Therefore, the authors should estimate “power” of study to rule out this query. Secondly, matching cases between two groups in an endocrinology study is critical. The authors matched groups in terms of age but menopausal status, age of menopause, race, menopausal hormone therapy, marital status, occupation, OCP use and etc should be matched. They demonstrated some demographic data for mentioned confounding factors but they did not state P-value for it to confirm matching between two groups. Thirdly, they measured only 25 (OH)2 vitamin D although it seems that measuring total 25-OH vitamin D levels (D (2) + D (3))can present a more valid serum level of vitamin D.[2] Also, some documents define terms of vitamin D deficiency and insufficiency different with this study which can justify differences between this study and them.[2] Moreover, Secondary cause of vitamin D deficiency in patients with BC such as Idiopathic hypercalciuria, primary hyperparathyroidism and normocalcemic hyperparathyroidism should be considered in these patients before any conclusion which was not enough considered by the authors.[3]

A newly considered aspect of relation between Vitamin D and neoplastic disorders such as breast cancer is role of Vitamin D Binding Protein (VDBP) in these diseases.[4] It was confirmed that lower level of vitamin D can be associated with higher incidence and worse prognosis.[5] The anti-neoplastic role of vitamin D can be due to enhancing effect of vitamin D on immune system which was weaken by alpha-N-acetylgalactosaminidase. Vitamin D binding proteins such as S100 and GC proteins group have a significant role in malignancy and neoplasm progression. The level of these proteins may be affected by serum level of vitamin D.[6] However, Gc-MAF (macrophage activating factor) as an activated vitamin D like proteins is a useful treatment for breast cancer which is less considered previously.[7] Therefore, when we want to discussed about the role of vitamin D in neoplastic disorders, it is also better to talk about its role in enhancing the immune system as system biology. Further study focusing on therapeutic effects of vitamin D derivates either as nutritional supplement for vitamin deficiency and also immunotherapy is required.