HMOX1 and neoplasm: Also, the observation that in malignant tumor cells, HO-1 can become truncated and localized to the nucleus to elicit a transcriptional-regulatory role provides an intriguing additional layer to the functionality of this protein, but highlights the need to consider the cellular localization of HO-1 rather than just its presence or absence in the TME (11, 16, 23, 44).