The lungs are a common site for metastasis of malignant tumors. According to statistics, 20%–30% of patients who die from malignant tumors are found to have pulmonary metastases. Common primary malignant tumors with a high propensity for lung metastasis originate from the gastrointestinal tract, liver, thyroid, breast, bones and soft tissues, as well as the skin. The timing of lung metastasis varies among different tumors. In most cases, metastasis occurs within three years of the development of the primary tumor, although in some instances, pulmonary metastases may appear more than five years after treatment of the primary tumor. In a small number of cases, pulmonary metastases are detected before the primary tumor is diagnosed. With extended survival due to advancements in cancer treatment and the adoption of regular follow-ups, the incidence and detection rate of pulmonary metastases have been gradually increasing.
Clinical Manifestations
Most patients with pulmonary metastases have no specific or overt clinical symptoms beyond those associated with the primary tumor. In general, they are detected during routine chest X-rays performed as part of follow-up examinations in patients with a history of primary malignancy. A minority of cases may present with symptoms such as cough, hemoptysis, fever, and dyspnea.
Diagnosis
The imaging characteristics of pulmonary metastatic tumors typically include multiple round peripheral lesions of varying sizes, homogenous density, and sharply defined margins. In some cases, only a single pulmonary lesion is present. A preliminary diagnosis of pulmonary metastases can usually be made based on findings from chest X-rays or chest CT scans, in combination with the diagnosis or history of the primary tumor. However, definitive diagnosis requires pathological confirmation.
Treatment
Surgical treatment for pulmonary metastatic tumors requires fulfillment of the following four conditions:
- The primary tumor must have been adequately treated or controlled.
- No other metastases should be present elsewhere in the body.
- The pulmonary metastatic tumors must be entirely resectable.
- The patient must be able to tolerate the required surgical procedure.
Surgical Techniques
The commonly employed surgical procedure for pulmonary metastases is wedge resection. In cases where the tumor is larger or located near the hilum, segmentectomy or lobectomy may be considered, while pneumonectomy should be approached with particular caution. For bilateral lesions, simultaneous or staged surgeries may be considered.
Prognosis
The therapeutic efficacy of surgery for pulmonary metastatic tumors is influenced by various factors. Incomplete resection is associated with poor prognosis. A longer interval between the resection of the primary tumor and the appearance of pulmonary metastases is generally linked to better prognosis. Conversely, a greater number of metastatic lesions correlate with poorer outcomes. Postoperative outcomes are also significantly affected by the immune status of the patient and the biological behavior of the primary tumor. Among patients with pulmonary metastases, those with metastatic tumors from colorectal cancer tend to have relatively favorable outcomes after surgical resection.