It has been reported that secondary tumours in cases of relapse after treatment are often multidrug-resistant.40 This observation may be attributed to an incomplete eradication of heterogeneous cell populations under targeted anti-cancer therapeutic strategies.41 Here, we support this observation by demonstrating an increase in proportion in CD44+/CD24− phenotype cells after exposure of cancer cell clusters to doxorubicin. The gene discussed is CD44; the disease is neoplasm.