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The incidence of metastases to the breast from nonbreast carcinoma is less than 1% of all breast cancers; of these, adenocarcinoma of the lung to breast is a small proportion (<0.1% of breast carcinomas). The imaging findings of a case of metastatic lung adenocarcinoma to the breast are presented with a review of the literature. Imaging findings including elastography suggesting the breast mass is not a primary breast cancer are highlighted. The importance of notifying the pathologist that nonbreast metastatic disease is in the differential is discussed. The use of appropriate tumor markers is needed; otherwise, the lesion may be interpreted as a triple negative breast cancer.

The association of hormonal syndrome and APUD (amine precursor uptake, decarboxylase) features with small cell carcinoma of the lung (SCC) has suggested that SCC has a separate cell origin from other major forms of lung cancer. Recently, however, both SCC and non-SCC lung cancers have been found to contain small polypeptide hormones and APUD enzymes. The present study quantitates, in 50 samples of human lung cancer tissue, relationships among the 4 major types of lung cancer and endocrine-related properties. Among 4 parameters measured (dopa decarboxylase, histaminase, beta-endorphin, and calcitonin), no single marker clearly separated SCC from non-SCC lung cancer. The high activity of dopa decarboxylase (the "D" in "APUD") best separated SCC from non-SCC, but significant overlap existed even for this critical APUD property. In fact, 2 adenocarcinomas had among the highest concentrations of dopa decarboxylase, histaminase, and calcitonin of any tumor tissue studied. The simultaneous appearance of high levels of 2 or more markers favored SCC. This was quantitated by deriving an index unit based upon the product of the values for the 4 markers in each lesion. This index separated all SCC from all non-SCC lung carcinomas, with the exception of the above 2 adenocarcinomas. Endocrine-related properties thus occur throughout the spectrum of human lung cancer. Biochemical differences between the major histopathological types are quantitative rather than qualitative and probably reflect the fact that the major forms of lung cancer represent a continuum of differentiation within a common cell lineage which includes both SCC and non-SCC lung tumors.

We have previously determined that the cell surface protein phenotype distinguishes human small cell lung carcinoma (SCC), a neoplasm with endocrine properties, from non-SCC in culture. We now demonstrate that cloned cell cultures of human large cell undifferentiated lung carcinoma, established directly from a patient with mixed SCC and non-SCC, simultaneously express surface proteins characteristic of SCC and non-SCC lung cancer cells. Hence, SCC and a form of large cell carcinoma appear linked through a continuum of differentiation events that: (i) may explain clinically important transitions that occur between the major types of human lung cancer and (ii) provide evidence for a common cellular origin of endocrine and nonendocrine cells in the bronchial mucosa.

To ascertain whether the content of endocrine markers is constant in small-cell carcinoma of the lung, levels of three markers of medullary thyroid carcinoma were studied in this tumor. Histaminase was increased in six of six primary tumors (three to 14,000 times), L-dopa decarboxylase in four of six (six to 30 times), and calcitonin in one of one (eight times) over levels in adjacent lung. Marker levels in mediastinal metastases reflected those in primary tumors in four of five patients. However, in four of seven, multiple hepatic metastases contained low to absent levels despite simultaneously high values in chest lesions. Immunohistochemical studies of histaminase revealed that within each primary tumor different cells contained different amounts of the enzyme. Since marker content varied between tumor cells, between primary tumors and between metastases in individual patients we conclude that circulating levels of these three markers cannot be expected necessarily to mirror tumor burden in patients with small-cell lung tumors.