HER2 - positive breast cancer is a subtype of breast cancer, which has higher expression of HER2 genes. HER2 is an abbreviation for human epidermal growth factor. The HER2 gene is important for synthesis of HER2 proteins. HER2 proteins are receptors on breast cells. HER2 receptors are important for control of normal and healthy breast cell grows and the mechanisms of repairing itself. In about 25% of breast cancers, the HER2 gene does not work correctly and makes too much copies of itself and it is called HER2 gene amplification. All these extra HER2 genes send signals to breast cells and their response is making too much HER2 receptors, which is called HER2 protein overexpression. It makes breast cells grow and divides it in an uncontrolled way. There are four tests for patients to establish if they have HER2 - positive breast cancer: IHC test, FISH test, SPoT – Light HER2 CISH test and Inform HER2 DUAL test. Treatment for that special kind of cancer includes four drugs: trastuzumab, trastuzumabemtanisine, partuzumab and lapatinib. The results of many pharmacoeconomic studies still give preference to trastuzumab (Herceptin®), humanized monoclonal antibody for human epidermal growth factor (HER2). Study for middle – income countries, made in Iran, concludes that six months therapy can be more cost effective than 12 months and the costs could be reduced for 40.000.000 €. On the other hand, trastuzumab therapy combined with taxanes is justified only if direct medical expenses are decreased for 50%. Pertuzumab (Perjeta®), humanized monoclonal antibody for HER2 protein, is the newest drug for HER2 – positive breast cancer. Studies showed that Perjeta® therapy is still not profitable if expenses are compared with trastuzumab. Monthly costs for Perjeta® therapy are 4.800 € and the same treatment with Herceptin® is 3.650 €. Also, duration of the therapy with Perjeta® is 18,1 months which in the end increases expenses up to 151.470 €. Results show that Perjeta® treatmant raises expenses for 4 billion € more than Herceptin® treatment in Canada. Good assessment of the illness and diagnosis of the stage can decrease expenses of the treatment. If oncologist would estimate metastatic breast cancer in the beginning of treatment and start with lapatinib (Tyverb®), dual tyrosine kinase inhibitor which interrupts the HER2 and epidermal growth factor receptor (EGFR) pathways, combined with capecitabine in therapy instead of Herceptin®, it would save 3.044 € per person in three years therapy.