Background The calpains are intracellular cysteine proteases that function in a variety of important cellular functions including signalling motility apoptosis and survival. cohort of early stage breast cancer patients (n?=?783) using immunohistochemistry on a tissue microarray. Patients experienced long-term follow-up information available for analysis. Results Low expression of calpain-9 was associated with patients over 40?years of age (; however this study clearly demonstrates that calpain-9 is usually expressed in invasive breast malignancy and is not expressed solely in a digestive tract specific manner. Low expression of calpain-9 was associated with patients over 40?years smaller tumour size and stage favourable NPI values and ER positive tumours. The calpain system in general has been implicated in tumour progression including altering cellular migration survival and apoptosis; and expression of calpain-1 calpain-2 and calpastatin have been shown to be important in breast malignancy [2 3 18 High calpain-2 expression in breast malignancy is usually associated with poor survival in patients with triple unfavorable or basal-like phenotype tumours; and high expression of calpain-1 can predict response following adjuvant trastuzumab therapy [2 3 In addition to breast malignancy expression of the calpain family has been explained in a number of solid tumour types [4-6]. Whilst the current study measured the expression of calpain-9 it cannot predict Maraviroc the activity of the enzyme; therefore no conclusions about the effect of calpain-9 activity can be made as a result of this research. Expression of calpain-9 was significantly associated with overall disease-specific survival in those patients with CYSLTR2 an intermediate NPI value whereas it was not associated with survival in those patients with good or poor NPI values. Calpain-9 expression remained significant for overall survival in patients with an intermediate NPI value even when potential confounding factors were included in the analysis. The NPI functions to stratify patients’ risk of 5?12 months recurrence and is used in decision making regarding chemotherapy. It is calculated from the size of the index lesion the number of positive lymph nodes and tumour grade. Patients with a high NPI are offered chemotherapy but it is usually often difficult to determine the best course of action for those with an intermediate NPI. Often in these cases decisions are based on the presence of other high risk features such as patient age tumour grade nodal involvement and vascular invasion. Our Maraviroc results show patients with Maraviroc an intermediate NPI experienced a significantly worse disease-specific survival if their tumours experienced low expression of calpain-9 which could be potentially examined in these patients to aid decision making on systemic treatment. Furthermore low expression of calpain-9 was associated with adverse disease-specific survival in those patients that received endocrine therapy. Expression of calpain-9 remained significant for disease-specific survival in this sub group of patients even when potential confounding factors were included in the analysis. There was no association between expression of calpain-9 and disease-specific survival in ER positive patients or patients with basal-like disease. Endocrine therapy is usually often offered to patients with ER positive disease perceived to have low risk disease on traditional clinicopathological features Maraviroc such as tumour stage and grade NPI and nodal status. Most tumours that in the beginning respond to endocrine therapies can acquire resistance which is a major obstacle for the successful management of ER positive tumours. Interestingly although tumours become resistant to endocrine therapy they can still maintain ER expression (examined in ). The expression of calpain family members has been implicated in ER signalling. An increase in calpain activity has been shown following treatment with 17β-oestradiol but also in ER positive tumours [8 9 You will find limited direct reports of ER modulating calpain-9 expression or activity. In lacrimal glands from mice which were treated with 17β-oestradiol and/or progesterone to determine differentially expressed mRNAs was shown to be down regulated . Calpain-8 has been shown Maraviroc to be stimulated by 17β-oestradiol in the.