Background: Invasive ductal carcinoma is the most common type of breast malignancy, with varying molecular features and resistance to treatment. Although CD44+/CD24- cells are believed to act as breast cancer stem cells and to be linked to poor prognosis in some patients, the association between these cells and tumor recurrence or metastasis in all or some types of invasive ductal carcinoma is unclear.

Methods: A total of 147 randomly selected primary and secondary invasive ductal carcinoma samples were assayed for expression of CD44, CD24, ER, PR, and Her2. The association between the proportions of CD44+/CD24- tumor cells and the clinico-pathological features of these patients was evaluated.

Results: CD44+/CD24- tumor cells were detected in 70.1% of the tumors, with a median proportion of 5.8%. The proportion of CD44+/CD24- tumor cells was significantly associated with lymph node involvement (P = 0.026) and PR status (P = 0.038), and was correlated with strong PR status in patients with recurrent or metastatic tumors (P = 0.046) and with basal-like features (p = 0.05). The median disease-free survival (DFS) of patients with and without CD44(+)/CD24(-/low) tumor cells were 22.9 ± 2.2 months and 35.9 ± 3.8 months, and the median overall survival (OS) of patients with and without CD44(+)/CD24(-/low) tumor cells were 39.3 ± 2.6 months and 54.0 ± 3.5 months, respectively, and with both univariate and multivariate analyses showing that the proportion of CD44(+)/CD24(-/low) tumor cells was strongly correlated with DFS and OS.

Conclusion: The prevalence of CD44+/CD24- tumor cells varied greatly in invasive ductal carcinomas, with the occurrence of this phenotype high in primary tumors with high PR status and in secondary tumors. Moreover, this phenotype was significantly associated with shorter cumulative DFS and OS. Thus, the CD44(+)/CD24(-) phenotype may be an important factor for malignant relapse following surgical resection and chemotherapy in patients with invasive ductal carcinoma.