Abstract P6-03-05: An Approach for the Differential Diagnosis of Primary Lung Cancer and Breast Cancer Relapse Presenting as a Solitary Pulmonary Nodule in Patients after Breast Surgery

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Abstract Background: The distinction of primary lung cancer from metastatic breast cancer is crucial in patients presenting with a solitary pulmonary nodule after breast surgery. However definitive diagnosis of these nodules is often difficult due to similar radiological and pathological features in primary lung and metastatic breast cancer nodules. We assessed the feasibility of our diagnostic approach for these nodules by morphopathological and immunohistochemical examination, and estimated the frequency of primary lung cancer occurrence in breast cancer patients. Material and Methods: We evaluated solitary pulmonary nodules appearing in 24 patients (0.62% : 24/3851) after breast surgery between 1994 and 2006. Patients with metastases to organs other than lungs were not included. For histological examination, CT-guided core needle biopsy (CT-CNB), trans-bronchial lung biopsy (TBLB), or surgical resection was performed. Besides conventional morphopathological examination using HE staining, differential diagnosis was performed by immunohistochemical examination (thyroid transcription factor-1: TTF-1, surfactant pro-protein B: SPPB, estrogen receptor: ER, mammaglobin1: MGB1). The immunopositive results for TTF-1 and SPPB support the specimen diagnosis of primary lung cancer. The immunopositive and immunonegative results for ER and both TTF-1 and SPPB, respectively, suggest that the specimen has a high probability of being metastatic breast cancer. And for cases in which differential diagnosis failed in the morpopathological and TTF-1, SPPB, and ER examination, MGB1 examination was conducted. Several patient and tumor characteristics were evaluated according to the definitive diagnosis of pulmonary nodules in both metastatic breast and primary lung cancer groups, which were then compared using Student's t-test. Results: Biopsy specimens were obtained using minimally invasive methods (CT-CNB and TBLB) in 21 patients (87.5%). Surgical resection was performed for diagnosis and treatment in three patients. Differential diagnosis was obtained by morphopathological methods alone in 18 patients (75.0%, primary lung cancer: 6 cases, metastaic breast cancer: 12 cases) and by immunohistochemical examination in the remaining 6 (25.0%, primary lung cancer: 1 case, metastaic breast cancer: 5 cases). Final diagnosis was metastatic breast and primary lung cancer in 17 (70. 8%) and 7 patients (29.2%), respectively. The mean age was significantly higher in the primary lung than metastatic breast cancer patients group (67 years vs. 57 years: p=0.036). No significant difference in the average diameter of pulmonary nodules was observed between metastatic breast and primary lung cancer patients (2.32cm vs. 2.29 cm). Furthermore, there were no clinical findings between metastatic breast cancer patients group and primary lung cancer group. Conclusions: Our results show the clinical feasibility of our approach to the differential diagnosis of breast cancer relapse and primary lung cancer presenting as a solitary nodule in patients after breast surgery. Further, replication of our findings under independent setting is recommended. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-03-05.