To assess the presence of ER stress with an orthogonal approach, we applied transmission electron microscopy to examine the changes in ER ultrastructure using four ovarian cancer cell lines with different TP53 state (human A2780 and murine ID8 are TP53 wild‐type ovarian cancer cell lines, while human OVCAR8 and HOC7 harbor mutant TP53). Here, TP53 is linked to ovarian carcinoma.