Medullary carcinoma of the breast: a tumour lacking keratin 19

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Abstract
The presence of keratin 19 (K19) was searched for by immunostaining in 16 medullary carcinomas, comprising 12 typical and four atypical cases, in 29 undifferentiated high‐grade carcinomas (NOS‐HG) with conspicuous lymphoid response and in 12 well differentiated low‐grade carcinomas (NOS‐LG). The medullary carcinomas were all negative whereas 23 of the high‐grade and all 12 low‐grade carcinomas expressed K19. Staining for K19 could be of value in the differential diagnosis of these tumours. Furthermore, these findings, with other observations, raise the possibility that medullary carcinoma cells could be linked to precursor cells of the terminal duct lobular units because both populations share several characteristics.