Background: FISH and immunohistochemistry (IHC) on formalin-fixed paraffin embedded (FFPE) tissue are currently used in the clinical laboratory to determine HER2 status in invasive breast cancer patients. Since tissue-based methods are relatively time-consuming and have a limitation for standardization of procedure, we evaluated the availability of fine needle aspirates (FNA) for the assessment of HER2 status in invasive breast cancer patients.
Methods: FNA were obtained from 51 invasive breast cancer patients and were submitted for the evaluation of HER2 status. After invasive breast cancer components were ascertained by morphological evaluation, HER2 gene amplification was evaluated by FISH. The results of HER2 FISH on FNA cells were compared with those of both FISH and IHC on corresponding FFPE tissues. FISH results were interpreted by American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines issued in 2007.
Results: Of 51 FNA specimens, one was excluded due to an insufficient number of cancer cells for tests. Excluding the cases that showed 'equivocal' results, 47 (98%) out of 48 cases were concordant between the results of FISH on FNA and FISH on corresponding FFPE tissue (kappa, 0.969), and 43 (93%) out of 46 cases were concordant between the results of FISH on FNA and IHC on corresponding FFPE tissue (kappa, 0.912).
Conclusions: An excellent correlation was found between FISH on FNA cells and corresponding FFPE sections. We recommend FNA specimens for more rapid determination of HER2 status by FISH, which will be helpful for patient selection for individualized therapy.