Leiomyomas with a collagen type IV alpha 5 chain (COL4A5) and collagen type IV alpha 6 chain (COL4A6) deletion resulting in overexpression of insulin receptor substrate 4 (IRS4) have been proposed as another leiomyoma subtype, but such aberrations have thus far been reported in only a small number of tumors.11, 13. Here, IRS4 is linked to leiomyoma.