HOXA1 and gastric cancer: The medium supernatant from senescent gastric cancer cells (MKN‐45 and HGC‐27) stably over‐expressing PITX2 or sh‐PITX2 #1 was collected to induce the increase or decrease in anchorage‐independent growth and invasive properties of cancer cells, which were rescued by stable knockdown or over‐expression of HOXA1 (Figure 6A,B; Figure S9D,E, Supporting Information).