Treatment Approach for FISH-Positive (HER2-Positive) Breast Cancer

Introduction to HER2-Positive Breast Cancer Treatment

The National Comprehensive Cancer Network recommends that HER2 testing should be performed on every primary invasive breast cancer to guide treatment decisions 2
Patients are considered HER2-positive if their tumors are either positive for HER2 by FISH or 3+ by IHC, as stated by the National Comprehensive Cancer Network 3, 4

The National Comprehensive Cancer Network recommends the combination of trastuzumab, pertuzumab, and a taxane as the standard first-line treatment 1, 3
Chemotherapy should continue for approximately 4-6 months or until maximal response, while HER2-targeted therapy should be continued until disease progression, according to the National Comprehensive Cancer Network 1
Alternative first-line regimens include trastuzumab with other chemotherapy agents such as vinorelbine or capecitabine, as recommended by the National Comprehensive Cancer Network 3, 4
The combination of trastuzumab with doxorubicin/cyclophosphamide should be avoided due to high risk of cardiac dysfunction, as warned by the National Comprehensive Cancer Network 3, 4

Cardiac monitoring should be performed before and during trastuzumab therapy due to risk of cardiotoxicity, as advised by the European Society for Medical Oncology 5
Response evaluation is recommended after 2-3 cycles of chemotherapy through clinical assessment, imaging, and tumor markers, according to the European Society for Medical Oncology 6
After completing chemotherapy in combination regimens, HER2-targeted therapy should be continued until disease progression or unacceptable toxicity, as recommended by the National Comprehensive Cancer Network 1

Failure to re-biopsy accessible metastatic lesions to confirm HER2 status can lead to inaccurate treatment, as noted by the National Comprehensive Cancer Network 1
Discontinuing HER2-targeted therapy prematurely after chemotherapy completion instead of continuing until disease progression is not recommended, according to the National Comprehensive Cancer Network 1
Using trastuzumab in combination with anthracyclines outside of clinical trials due to high risk of cardiac toxicity is warned against by the National Comprehensive Cancer Network 3, 4
Inadequate standardization and validation of HER2 assays can lead to false-positive determinations, as cautioned by the National Comprehensive Cancer Network 3, 4