Original Articles High Expression of LMTK3 is an Independent Factor Indicating a Poor Prognosis in Estrogen Receptor a-Positive Breast Cancer Patients

Objective: Over 70 % of breast cancers are estrogen receptor alpha-positive, and endocrine therapy targeting estrogen action decreases mortality from breast cancer. Recently, a novel protein kinase that regulates estrogen receptor alpha activity, lemur tyrosine kinase-3, has been identified. In this study, we investigated whether messenger RNA expression and polymorph-isms of the gene encoding the kinase, LMTK3, are associated with prognosis in breast cancer patients during long-term follow-up. Methods: First, we investigated the relationship between messenger RNA expression of LMTK3 and patient outcome in 219 breast cancers. The effects of several variables on survival were tested by Cox proportional hazards regression analysis. Next, we performed LMTK3 geno-typing in 471 breast cancers to clarify the prognostic role of these polymorphisms. Results: Our data showed that LMTK3 expression level was not associated with prognosis in all patients. We then analyzed the impact of LMTK3 mRNA expression on the prognosis of breast cancer according to estrogen receptor alpha status. Both disease-free survival and overall survival were significantly shorter in estrogen receptor alpha-positive patients with high LMTK3 expression receiving adjuvant endocrine therapy than in those patients with low LMTK