Metastatic adenocarcinoma to the breast from the lung simulates primary breast carcinoma—a clinicopathologic study

BACKGROUND: Rare extra-mammary metastases of adenocarcinoma to the breast closely mimic primary invasive breast carcinoma (PBC), and specifically without an aware of clinical history, pose a difficult diagnostic issue. METHODS: With the aim to improve differential diagnosis of lung adenocarcinoma metastasis and primary breast carcinoma in the breast, we retrieved 41 breast metastases from lung adenocarcinoma, seven of which were from the archived pathologic files of Cancer Hospital, Chinese Academy of Medical Science (CHCAMS) between 2001 and 2019, and the other 34 cases were collected from the published literatures. Clinicopathological features were collected and analyzed for differential diagnosis of primary lung malignancy, triple negative breast pathology and breast lesions without ipsilateral axillary lymphadenopathy or with contralateral axillary lymphadenopathy. Supplementary breast (GCDFP-15, or GATA-3) and lung-lineage (TTF-1) immunostaining plus genetic alternation analysis were also recorded and analyzed. RESULTS: Among the 41 cases, there were 37 females and four males, with a median age of 63 (range, 40–81) years at diagnosis of the breast lesion. Twenty-four cases (58.5%, 24/41) were detected metachronously to the counterpart of the lung. Strikingly, 13 cases (31.7%, 13/41) were initially misdiagnosed as primary breast cancer, and differential diagnostic factors were compared and analyzed between the correct and misdiagnosed cases, among which a documentation of lung cancer history showed significant difference. Pathologist initially misinterpreted six cases (46.2%, 6/13) as PBC on needle biopsy of breast mass with an unknown lung cancer history. The clinical diagnosis was considered two cases (15.4%, 2/13) to be either a primary breast tumor with lung and pleural metastasis or two synchronous primary tumors. Three cases (23.1%, 3/13) were initially misinterpreted as PBC by breast ultrasonography. TTF-1 immunostaining was found to be critical for a correct diagnosis of metastatic lesion (84.6%, 11/13) from the initially misdiagnosed cases as PBC. CONCLUSIONS: Metastatic lung adenocarcinoma to the breast, although rare, should be considered in the differential diagnosis of primary breast carcinoma, especially when the breast lesion exhibits as a “triple-negative invasive carcinoma”. A documented lung cancer history combined with the clinicoradiological assessment and pathological evaluation are essential to make a correct differential diagnosis. TTF-1 immunostaining is crucial in approaching the diagnosis.