Activation of mutated KRAS in transplanted endometrium triggers endometriosis in mice.32 Similarly, we have shown that a polymorphism of a Let‐7‐binding site in KRAS 3′‐UTR causes abnormal KRAS expression as well as increased proliferation and invasion in endometriosis.16 Let‐7b regulates KRAS expression by binding to one or more of 10 Let‐7 complementary sites (LCS) in the 3′‐UTR of the KRAS gene.33 Here, we show that both the KRAS 4A and 4B isoforms as well as total KRAS protein expression levels were diminished in the Let‐7b treatment group. Here, KRAS is linked to endometriosis.