RESUMO
BACKGROUND: The sentinel lymph node (SLN) is the first lymph node to receive the lymphatic drainage of a primary tumour; based on the knowledge that CK19 is positive in more than 95% of breast carcinomas, a molecular method for intraoperative diagnosis of SLN metastases (the one-step nucleic acid amplification (OSNA) assay) was developed. AIMS: To evaluate CK19 immunoreactivity in a series of special histological types of breast carcinoma in order to verify whether the OSNA assay can be used in all breast cancer cases independently of the histological type. METHODS: 116 samples of invasive breast carcinomas of special type were investigated for CK19 immunoreactivity in tissue microarrays (TMA); negative cases were evaluated in the entire tissue tumour tissue. RESULTS: Of the 116 cases, 88.9% were positive CK19. Micropapillary and apocrine carcinomas were all positive for CK19 in TMAs. The tubular (93%), mucinous (86%), medullary typical and atypical (84%), mixed carcinomas (83%) increased the rate of positivity for this marker to 100% after repeating the immunostain in whole tissue of negative TMA cases, because the expression of those cases was focal. CONCLUSION: Most breast cancer cases were positive for CK19, independent of the histological type; therefore the OSNA assay can be used in all breast cancer cases with a potential low rate of false negative for CK19 detection of micrometastasis. There is an important variation between the positivity assessed on TMAs and the entire tissue; these findings can be clinically relevant because in some cases CK19 is evaluated on core-needle biopsy prior to surgery.
