Metastatic thoracic lymph node carcinoma with unknown primary site.

BACKGROUND

Metastatic cancer in thoracic lymph nodes without a primary site is rare. The purpose of this study is to draw attention to this probably underestimated entity, to speculate on its possible origins, and to suggest guidelines for its treatment.

METHODS

Eight heavy smokers with no past medical history of cancer were diagnosed at operation to have malignant cells in intrathoracic lymph nodes (N1 or N2) with no primary site in the lung. All patients underwent an exploratory thoracotomy with a presumed diagnosis of lung cancer except one who presented with a middle lobe mucosa-associated lymphoid tissue lymphoma. We reviewed the type of surgical resection, histologic and immunohistochemical analysis of resected specimens, treatments, survival, and long-term results.

RESULTS

Resections performed were pneumonectomy (n = 4), lobectomy (n = 3), and bilobectomy (n = 1). All patients underwent complete mediastinal lymph node dissection. Lung resection was performed for mucosa-associated lymphoid tissue lymphoma (n = 1) and for tumorlike lesions that appeared to be tuberculoma (n = 1) and intrapulmonary metastatic lymph nodes (n = 6). Malignant cells were located in intrapulmonary lymph nodes alone (n = 3) or also in mediastinal lymph nodes in three other cases. All these tumors were cytokeratin-positive, demonstrating their epithelial nature. Pulmonary origin was confirmed in two cases (thyroid transcription factor 1-positive and thyroglobulin-negative). No other origin could be demonstrated by immunochemistry. Three patients died within the first year. All other patients are still alive without recurrence (Kaplan-Meier 5-year survival rate, 62.5%).

CONCLUSIONS

Frequency of metastatic cancer in thoracic lymph nodes without a primary site is probably underestimated because the cancer is routinely diagnosed by mediastinoscopy and considered as metastatic disease not amenable to operation. The origin of the disease, either pulmonary, endogenous, or from extrathoracic sites, is often difficult to assess. Nevertheless, our data confirm those of the literature and demonstrate that survival can be increased by operation. This implies diagnosis of the entity and consideration that thoracic lymph node involvement can apparently be isolated and therefore resectable.