Reduced expression of QSOX1 leads to a significant decrease in tumor cell growth. a) Western blot showing weak expression of QSOX1 in transformed, but non-tumor-forming MCF10A and human breast ductal carcinoma cell lines Luminal A like (MCF7 and MDA-MB-453), Luminal B like (ZR75 and BT474) and Basal like (BT549 and MDA-MB-231). α-Tubulin loading control is shown below each lane. MCF7, BT549 and BT474 breast tumor cell lines were transduced with lentiviral shRNA QSOX1 (sh742 and sh528). Western blots are shown using the same anti-QSOX1 polyclonal Ab as in Figure 2 on cell lysates from b.) MCF7 (percent decrease in sh742: 85% and sh528: 82%); c.) BT549 (percent decrease in sh742: 45% and sh528: 77%) and d.) BT474 (percent decrease in sh742: 40% and sh528 36%) cells. Western blots have been cropped and full images can be viewed in Additional file 1. (e-g) MTT and (h-j) Trypan Blue growth assays on MCF7, BT549 and BT474 cells transduced with shScramble, sh742 and sh528 assayed on Days 1 through 5. Percent decrease sh742 and sh528 day 5: e.) 66% (both); f.) 78% and 69%; g.) 52% and 34%; h.) 72% and 73%; i.) 98% and 96%; j.) 50% (both). Experiments were performed three times in triplicate; error bars represent SD from triplicate wells. Significance **, P < 0.01.