MYOEPITHELIAL CELLS IN CARCINOMA OF HUMAN BREAST

KIRITI SARKAR, M.B.B.S.,* AND ERNST KALLENBACH, PH.D.t From the Department of , McGill University, Montreal, Canada In ducts and alveoli of the normal mammary , contractile ele- ments of epithelial origin (myoepithelial cells) are located between the and . In the ducts myoepithelial elements appear as elongated cells, arranged like the turns of a screw.' They are spaced apart from one another except for occasional points of contact. With the increased number of ducts and alveoli occurring in the lactating gland, these cells also increase in number while retaining their architec- tural arrangement. They contain myofibrils which endow them with contractility and thus help in the ejection of milk.2 Several observers have described myoepithelial proliferation in vari- ous pathologic lesions of the human breast, for example, in benign lesions such as fibroadenoma,3-5 fibrocystic disease,3-5 and gynecomastia in males.5 The mixed tumor of the , frequent in the bitch though extremely rare in the human, contains numerous myoepithelial cells.3'4 While it has been postulated that these cells may become malig- nant and take part in forming the neoplastic stroma in so-called "car- cinosarcoma" of mammary ,4 it is widely held that they are absent in such common carcinomas as ductal carcinoma.5 With hematoxylin and eosin staining, the appears to be small and fusiform, its long axis being parallel to the basement membrane. It takes up a much darker stain than the ductal epithelium; the myofibrils are not discernible and even the nuclear-cytoplasmic demarcation is not prominent. A special staining procedure, the tannic acid-phosphomolybdic acid- amido black (TPA) technique of Puchtler and Leblond6 has been found to be particularly suitable for staining myofibrils and thus demonstrating myoepithelial cells.7 Forty cases of infiltrating ductal carcinoma were studied with this technique. The observations differed from those of pre- vious workers, in that myoepithelial cells were seen to be generally pres-

This work was supported by a grant from the National Institute of Canada to Dr. C. P. Leblond. Accepted for publication, April 6, i966. * Resident in Clinical Pathology, Pathology Institute, Dalhousie University, Halifax, Nova Scotia, Canada. t Assistant Professor, Department of Anatomy, College of Medicine, University of Florida, Gainesville, Fa.

301 302 SARKAR AND KALLENBACH Vol. 49, No. 2 ent in ductal carcinoma. The relative number of myoepithelial cells varied with the degree of differentiation of the tumor; they were present both at the site of origin of the tumor and in metastatic lesions in axillary lymph nodes. Thus, myoepithelial cells may be closely associated not only with normal but also with neoplastic epithelium in the mammary gland. MATERIAL AND METHODS Forty primary lesions and 3 cases with metastatic lymph node neoplasms from in- filtrating ductal carcinoma were collected as biopsy or radical mastectomy specimens. Metastatic lesions in the liver were obtained at necropsy from 2 patients who had died from diffuse carcinomatosis of the breast. The tissues were fixed in Carnoy's fluid for 24 hours and later transferred to 70 per cent alcohol. They were dehydrated in 85 per cent and absolute alcohol followed by methyl benzoate-celloidin and benzene, and were infiltrated in paraffin in vacuo at 56' C. Sections were cut at 3 ,u and were stained by the tannic acid-phosphomolybdic acid-amido black (TPA) method.8 Only infiltrating ductal carcinomas were selected for the present study, all of them originat- ing in postmenopausal women. Normal breast tissue from necropsy cases of the same age group was obtained as control material. RESULTS AND DISCUSSION The TPA technique stained the myofibrils of myoepithelial cells an intense blue-black. In contrast, epithelium was stained pale green and connective tissue fibers, pale yellow. Myofibrils were located at the periphery of myoepithelial cells, with the nucleus in a central position (Fig. 2). In the normal postmenopausal gland, smooth muscle (staining in a manner similar to that of myoepithelHal cells) was found in the walls of blood vessels, but was not seen in the fibrous stroma. The specimens of ductal carcinoma included ductal epithelium in various stages of malignant change. In most specimens, well differen- tiated ducts were present in addition to the more anaplastic strands and columns of infiltrating tumor cells. The ductal structures consisted of sharply outlined masses of tumor cells surrounded by a basement mem- brane. These residual ducts invariably contained myoepithelial cells which retained their usual location between basement membrane and tumor cells (Fig. i). Neoplastic cells infiltrating the stroma were arranged in single strands or cords and in small and large columns lacking a continuous basement membrane. Myoepithelial cells, when present, were not necessarily ap- plied to the surface of these cellular collections; discernible clefts were often present between tumor cells and myoepithelial cells, which thus appeared to be scattered within the scirrhous stroma between the infil- trating cords or columns of tumor cells (Figs. 4 and 5). Finally, if the area of infiltration was markedly cellular with a minimal amount of stroma, TPA stained cells tended to be absent (Fig. 3). Bizarre con- Aug., 1966 MYOEPITHELIAL CELLS 303 figurations and abnormal mitoses were not encountered in the myoepi- thelial cells. It would appear then that two factors influence the presence of myo- epithelial cells in ductal carcinoma: the occurrence of well defined neoplastic ducts and the amount of dense connective tissue. Thus, zonal hyperplasia of the ductal system and a reactive hyperplasia of stromal connective tissue might be factors contributing to the presence of these cells. In the 3 examples of metastatic carcinoma in lymph nodes examined neither a semblance of ductal structure nor scirrhous stroma were en- countered. Yet, myoepithelial cells were again situated at the periphery of the columns of tumor cells (Figs. 6 and 7), although they were sig- nificantly fewer in number than in the original neoplasm. Myoepithelial cells were not found in those portions of the nodes uninvolved by tumor. The presence of myoepithelial elements in lymph nodes with metastases might signify that the neoplastic epithelium stimulated the growth of these cells in this location. In the 2 examples of metastatic mammary carcinoma in the liver no myoepithelial cells were detected. Unfortu- nately, the original tumors were not available for examination; hence, the similarities between the original tumor and the metastatic lesions could not be established.

SUMMARY Myoepithelial cells, the flat or spindle-shaped contractile cells nor- mally present in the walls of the alveoli and ducts of the mammary gland, have been reported to be absent in malignant epithelial neoplasms such as ductal carcinoma. With the tannic acid-phosphomolybdic acid-amido black staining technique, however, it was shown that myoepithelial cells were frequent in ductal mammary carcinoma, their number being greater in tumors with ductal structure and with greater amounts of scirrhous stroma. They were also found, though in fewer numbers, in metastatic lesions in axillary lymph nodes, a fact confirming their close association with malignant neoplastic as well as with normal breast epithelium.

REFERENCES i. EGGELING, H. v. Die Milchdriise. Handb. D. Mikr. Anat. D. Menschen. v. MOEL- LENDORFF, (ed.). Vol. 3, pt. I, Springer, Berlin, 1927. 2. RICHARDSON, K. C. Contractile tissues in the mammary gland, with special ref- erence to myoepithelium in the goat. Proc. Roy. Soc. [Biol.], I949, 136, 30-45. 3. BiGGs, R. The myoepithelium in certain tumours of the breast. J. Path. Bact. I947, 59, 437-444. 4. HAmPERL, H. t'ber die Myothelien (epithelialen Elemente) der Brustdriuse. Virchow Arch. Path. Anat., 1939, 305, I71-215. 304 SARKAR AND KALLENBACH Vol. 49, No. 2 5. KUZMA, J. F. Myoepithelial proliferations in the human breast. Amer. J. Path., I943, I9, 473-489. 6. PUCHTLER, H., and LEBLOND, C. P. Histochemical analysis of cell membranes and associated structures as seen in the intestinal epithelium. Amer. J. Anat., I958, I02, I-3I. 7. LEBLOND, C. P.; PUCHTLER, H., and CLERMONT, Y. Structures corresponding to terminal bars and terminal web in many types of cells. Nature (London), I960, i86, 784-788. 8. KALLENBACH, E.; CLERMONT, Y., and LEBLOND, C. P. The cell web in the ameloblasts of the rat incisor. Anat Rec., I965, I539 55-70. We thank Dr. C. P. Leblond for his encouragement and helpful criticism.

LEGENDS FOR FIGURES Photomicrographs were prepared from sections stained by the TPA stain. FIG. i. Infiltrating ductal carcinoma. The figure-eight structure represents a neo- plastic . A TPA stained layer of myoepithelial cells appears at its base (ar- rows). The large, pale cells, both inside the ductular structure and outside in the connective tissue, are neoplastic. X 420. FIG. 2. A close-up view of the duct depicted in Figure I. An unstained nucleus (n) of a myoepithelial cell exhibits myofibrils on both sides (arrows). X I,300. FIG. 3. Infiltrating ductal carcinoma. A very cellular, infiltrating area of the tumor contains a minimal amount of stroma. No myoepithelial cells are apparent in this field. The structure with a lumen on the left is a capillary. X 620. Aug., I966 MYOEPITHELIAL CELLS 305

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FIG. 4. Infiltrating ductal carcinoma. Between two cell columns (C) connective tissue stroma (S) extends across the photograph. Myoepithelial cells appear not only at the surface of the cell columns (horizontal arrow at the base of the photograph), but also extend into the stroma (vertical arrows). A cleft ap- pears between tumor and myoepithelial cells. X I,300. FIG. 5. Infiltrating ductal carcinoma. Stroma in an infiltrating area contains myo- epithelial cells arranged in layers. The large cells at the top and bottom of the photograph are infiltrating cancer cells. X I,300. Aug., I966 MYOEPITHELIAL CELLS 307

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FIG. 6. Lymph node in the axilla containing metastases from an infiltrating ductal carcinoma. A solitary myoepithelial cell (arrow) may be seen at the surface of a cell column (C). The cells at left are lymphocytes (L). X I,300. FIG. 7. A different area in the same lymph node shown in Figure 6 exhibits a row of myoepithelial cells on the surface of a cell column (arrows). X I,100.