Surprisingly, section staining with αSMA antibody that is commonly used to identify fibroblasts (see control staining in Supplementary Figure S2A) marked a sub-membrane moiety of ovarian cancer cells, mainly at the inner surface of spheroids (Figure 4), in most instances evidently overlaying the EpCAM staining (Figure 5A,B). Here, ACTA1 is linked to ovarian carcinoma.