During metastatic progression, circulating cancer cells become lodged within the microvasculature of end organs, where most die from mechanical deformation. Although this phenomenon was first described over a half-century ago, the mechanisms enabling certain cells to survive this metastasis-suppressive barrier remain unknown. By applying whole-transcriptome RNA-sequencing technology to isogenic cancer cells of differing metastatic capacities, we identified a mutation encoding a truncated form of the pannexin-1 (PANX1) channel, PANX1(1-89), as recurrently enriched in highly metastatic breast cancer cells. PANX1(1-89) functions to permit metastatic cell survival during traumatic deformation in the microvasculature by augmenting ATP release from mechanosensitive PANX1 channels activated by membrane stretch. PANX1-mediated ATP release acts as an autocrine suppressor of deformation-induced apoptosis through P2Y-purinergic receptors. Finally, small-molecule therapeutic inhibition of PANX1 channels is found to reduce the efficiency of breast cancer metastasis. These data suggest a molecular basis for metastatic cell survival on microvasculature-induced biomechanical trauma.