Background Retrospective studies show significant improvements in survival among women who had breast cancer resected during the luteal phase of their menstrual cycle compared with the follicular phase.We hypothesised that tumour tissue would show cyclical changes in expression of genes whose products might contribute to metastatic potential.
Methods We studied 32 premenopausal women with operable breast cancer.We assayed hormones to define more accurately the menstrual phase during which surgery was done. We used northern blot analysis of RNA from fresh-frozen tumour specimens to study the patterns of expression of genes for proteolytic enzymes (cysteine proteinase cathepsin L and aspartyl proteinase cathepsin D; matrix metalloproteinases MMP-9 and MMP-2), tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2, and TP53.
Results There was a significantly higher level of expression of RNA for cathepsin L, MMP-9, and TP53 (p=0.005, 0.03, 0.03, respectively) in tumours that were resected during the follicular and periovulatory phases of the menstrual cycle than at other times in the cycle. A similar but non-significant trend was seen for MMP-2 and cathepsin D. A non-significant trend in the opposite direction was seen for TIMP-1 and TIMP-2.
Interpretation We found that tumour expression of genes that may contribute to proliferative capacity and metastatic potential can change in breast cancer during the course of the menstrual cycle.The finding could provide a molecular explanation for the reports of improved survival in some breast-cancer patients whose tumours were removed during the luteal phase of the menstrual cycle. Larger studies are required to extend our study, assess mechanisms of gene regulation, and verify any relevant influence in long-term survival.