SMAD4 and neoplasm: To understand if tumor cell intrinsic BMP signalling requires SMAD4 for suppression of metastasis and to eliminate the paracrine influence of secreted BMP4 on stromal cells, we generated tumor cells with a constitutively active Type Ia BMP receptor, BMPR1aQ233D (caBMPR1a), thereby removing the requirement for BMP4 to initiate the signalling.