CD44 and neoplasm: Fig. 4A shows a representative mouse with progressive muscle invasion by a tumour that paralysed its hind limb. HE histological staining of the mass identified an invasive tumour within the muscle that was consistent with a poorly differentiated adenocarcinoma. Moreover, histological differences were observed between the CD44+ and CD44− tumours. The CD44+ tumours with larger, irregular and hyperchromatic nuclei were more heterogeneous (Fig. 4B).