In this work, we discovered that a naturally occurring β-(1, 3)-D-glucan from Lentinus edodes coded as LNT not only selectively inhibited proliferation of MCF-7 and T47D breast cancer cells positively expressing ERα in vitro, but also suppressed MCF-7 tumor growth with the inhibition ratio of over 50% via suppressing cell proliferation and promoting cell apoptosis in vivo. The gene discussed is ESR1; the disease is neoplasm.