BACKGROUND.Transforming growth factor β (TGFβ) is important in colorectal cancer (CRC) progression. Bone morphogenetic proteins (BMPs), a subgroup within the TGFβ superfamily, recently also have been implicated in CRC, but their precise role in CRC has yet to be investigated.METHODS.The authors used a tissue microarray and immunohistochemistry of BMP receptors and signal transduction elements in adenomas and CRC specimens to elucidate the role of BMP signaling in CRC carcinogenesis.RESULTS.The adenoma specimens expressed all 3 BMP receptors (BMPRs) (BMPR type 1a [BMPR1a], BMPR1b, and BMPR2) and expressed SMAD family member 4 (SMAD4); and 20 of 22 adenomas (90.9%) exhibited active BMP signaling, as determined by nuclear phosphorylated SMAD1,5,8 (pSMAD1,5,8) expression. In contrast, pSMAD1,5,8 nuclear staining was present in 5 CRC specimens (22.7%) but was lost in 17 CRC specimens (77.3%; cancer vs adenoma; P < .0001). The earliest loss of pSMAD1,5,8 nuclear staining was detected in regions of high‐grade dysplasia/carcinoma in situ within adenomas. CRCs showed frequent loss of BMPR2 (P < .0001) and SMAD4 (P < .01) compared with adenomas. Negative expression of BMPR2 was observed more frequently in earlier stage cancers (Dukes stage B) than in advanced cancers (Dukes stage C; P < .05).CONCLUSIONS.Taken together, the current results indicated that loss of BMP signaling correlates tightly with progression of adenomas to cancer and occurs relatively early during cancer progression. Cancer 2008. © 2007 American Cancer Society.