Handedness and breast cancer characteristics

Around 10% of the population is left-handed (LH) and the new data suggests that there is genetic as well as environmental influence on the hand preference. The purpose of this study was to evaluate the relationship between breast cancer and hand preference.

Breast cancer patients diagnosed and treated at the Department of Medical Oncology, Hacettepe University, Institute of Oncology between March 2006 and May 2010 were included in the study. The preferred handedness was asked in all patients and recorded in the patients' medical database.

A total of 898 patients with breast cancer were analyzed for handedness, basic characteristics and survival. The median age was 48 years (range 20-83) and all but one patient were female. Of all, 434 (48.3%) patients were pre, 61 (6.8%) were peri, and 399 patients (44.4%) were postmenopausal. Nearly all of the patients (n=869, 96.7%) were operated and modified radical mastectomy was the most frequent type of surgery (N=654, 72.8%). Invasive ductal carcinoma was observed in 659 (73.3%) and in 659 patients (73.1%)estrogen receptors (ER) were positive. Similarly 569 (63.4 %) patients were progesterone receptor (PR) positive and 181 (20.2%) had HER2 overexpression. Most of the patients had T2 (434; 48.3%), N0 (376; 41.9%) and M0 (830; 92.4%) tumors. Of all, 55 (6.1%) patients were LH and the remaining 843 (93.9%) were right-handed (RH). There was no statistically significant difference between the groups related to ER or PR status, TNM classification, tumor localization, menopausal status, HER2 or histological subtype. However the median age of diagnosis in right-handers was higher (48-46 years, p=0.02). There were 10 (1.1%) patients who had already passed away at the time of analysis. The mean overall survival (OS) for RH patients was 33 months (range 1-281) and for LH patients it was 35 months (range 1-182) (p=0.751). The disease disease-free survival (DFS) was 29 months for both groups (p=1.00).

In our trial the onset of breast cancer was 2 years earlier in LH patients with similar disease characteristics compared to RH patients. As a consequence, it may be advocated that the screening of LH patients should start earlier.