Most drugs have data only from clinical trials focused on a specific population at the time of first registration, so their indications for use are restricted to this population. In Brazil, the prices of new drugs for clinical conditions with no therapeutic alternatives are relatively high. When these drugs expand to other indications their prices are not reviewed, which can have a major financial impact. This study aimed to evaluate the financial impact of expanding the indication for trastuzumab deruxtecan.

We calculated the annual cost to treat all Brazilian patients with the indications listed for trastuzumab deruxtecan at first registration, and then all additional indications. Populations were estimated from epidemiological data from National Committee for Health Technology Incorporation reimbursement documents and a clinical trial comparing trastuzumab deruxtecan with trastuzumab emtansine. Costs were calculated using the ANVISA Câmara de Regulação do Mercado de Medicamentos price value and a patient weight of 70 kg.

In January 2022, trastuzumab deruxtecan was introduced in Brazil for patients with human epidermal growth factor receptor (HER2) positive metastatic or unresectable breast cancer who had received two or more anti-HER2 treatment regimens. In June 2022, the indication was expanded to patients with HER2-positive metastatic or unresectable breast cancer who had received one anti-HER2 treatment regimen. In November 2022, the indication was further expanded to patients with metastatic or unresectable low-expression HER2 breast cancer who had received prior systemic therapy. The number of patients estimated to be eligible for the drug increased from 383 to 23,000, with an increased total cost from BRL467,970,786 (USD90,621,763) to BRL26,048,234,160 (USD5,044,197,164).

The expansion of indications for trastuzumab deruxtecan may substantially increase its financial impact and compromise the sustainability of health systems. In Brazil, the lack of monitoring of drug prices means that the only change in prices occurs due to regulated annual inflation adjustments. Regulation is needed to reduce drug prices according to new indications, changes in therapeutic options for the same condition, and obsolescence.