Clinical relevance and low tumor-initiating properties of oligometastatic breast cancer in pulmonary metastasectomy.

Metastatic breast cancer is a systemic disease. However, certain subsets of patients, such as those with oligometastatic breast cancer (OMBC), have long-term survival prospects. Our aim was to evaluate the clinical relevance of OMBC in pulmonary metastasectomy of recurrent breast cancer. We also investigated lung metastases for the prevalence of CD44+/CD24-/low tumor cells and evaluated their prognostic significance. We reviewed data from a registry of breast cancer patients with lung metastases who underwent pulmonary metastasectomy at Jikei University Hospital. We analyzed prognostic factors for overall survival (OS) and progression-free survival (PFS) after metastasectomy and examined the prognostic difference between OMBC and non-OMBC patients. CD44+/CD24-/low tumor cells were detected by immunohistochemical analysis of lung metastases sites. Among 17 breast cancer patients with lung metastasis, 5-year OS and PFS rates were 72 and 36 %, respectively. Better OS was observed among patients with OMBC. Patients with OMBC, estrogen receptor-positive cells, and disease-free intervals of >8 years had better PFS. The presence of CD44+/CD24-/low tumor cells influenced progression after lung metastasectomy, with median PFS of only 6 months in patients with a high prevalence of cancer-initiating cells. CD44+/CD24-/low cells with cancer-initiating properties were present in only 9 % ± 3 of patients with OMBC, but were found in 73 % ± 12 of patients with non-OMBC. Pulmonary metastasectomy may be a treatment option for OMBC patients with lung metastases. Better prognosis of OMBC may be associated with low levels of cancer-initiating cells.