The biggest difference between WT and STAT3 KO was observed in SKOV3 and OVCAR3 xenografts: the tumor did not grow after KO of STAT3. Immunohistochemical staining of SKOV3 tumor tissues revealed significant histologic differences between the WT and STAT3 KO tumor specimens (Figure 2E, a full pathology report is provided in Supplemental data 1). STAT3 KO tumors were composed of fewer tumor cells within a more abundant collagenous stroma, while WT tumors presented with abundant tumor cells with vacuolated cytoplasm within a scant fine fibrovascular stroma. Here, STAT3 is linked to neoplasm.