To begin to clarify which aspects of CD151's α3β1 integrin-regulatory functions may depend on which other TEM-resident proteins, we created breast carcinoma cells with profound RNAi-mediated silencing of CD9 and CD81, two closely related tetraspanins that engage in similar biochemical interactions [38]–[42] and which strongly depend on CD151 for association with α3β1 [30], [35], [43], [44]. This evidence concerns the gene CD9 and breast carcinoma.