Surgical therapy for pulmonary metastasis of breast cancer

Metastatic breast cancer (MBC) is a disease with heterogeneous manifestations that arise from a variety of modes of spread from the primary disease. The lung is a common site of metastasis from breast cancer. A solitary lung nodule appearing on radiological examination following breast cancer treatment is likely to be diagnosed as pulmonary metastasis from breast cancer. However, the reported final pathological diagnoses include primary lung cancer and MBC in approximately 48-67% and 23-43% of cases, respectively. Moreover, some pulmonary metastases of breast cancer have radiological and histological characteristics similar to those of primary lung cancer. Thus, the differential diagnosis of a solitary lung nodule after treatment of breast cancer is challenging. Oligometastatic disease (OMD) is characterized by solitary or limited numbers of detectable metastatic lesions. OMD in the lung from colorectal cancer can be considered for locoregional treatments either alone or in combination with systemic therapy. In MBC patients, the indication for locoregional treatments for pulmonary metastasis is controversial, whereas surgical intervention can be performed to obtain tissue for histological and molecular confirmation and occasionally for curative intent in selected MBC patients. While several retrospective studies have examined the clinical impact of pulmonary metastasectomy (PM) in MBC patients, no prospective randomized trials have been conducted. Our systematic review of PM in MBC patients found that PM might offer a survival advantage in selected MBC patients with a long disease-free interval (DFI), small number of pulmonary metastases, complete resection, and/or hormone receptor positivity. Metastases are usually detected by radiological examinations such as computed tomography (CT) and positron emission tomography-CT. The detectability of these radiological examinations mainly depends on tumor size (size-dependent manner). By contrast, the amount of circulating tumor DNA (ctDNA) released by apoptotic or necrotic tumor cells depends on the tumor burden in the whole body, regardless of radiological detectability (dose-dependent manner). Since ctDNA assays reportedly reveal residual disease several weeks earlier than radiologic imaging does, monitoring for radiological tumor size and ctDNA concentration during the clinical course may help to inform the indication for local treatment in patients with MBC and may improve their clinical outcomes. This article reviewed the current status of PM in MBC patients with pulmonary metastasis and discussed future perspectives.