Introduction

Breast cancer is the most prevalent malignancy among women worldwide, with an age-standardized rate of 46.8 per 100,000 and represents an important health burden (WHO International Agency for Research on Cancer, 2022).

In Italy, the incidence of breast cancer has been steadily increasing, with approximately 55,900 new cases diagnosed in 2022 (Lei et al., 2021; AIRTUM, 2023).

HER2-positive breast cancer, characterized by overexpression of the human epidermal growth factor receptor 2, constitutes about 20%–25% of all breast cancer cases and is associated with a more aggressive disease course and poorer prognosis (Slamon et al., 1989; Harbeck et al., 2019).

The treatment landscape for breast cancer (von Arx et al., 2023), particularly concerning biologically originated oncological medications, has witnessed significant evolution in recent years. Among these medications, trastuzumab stands as a cornerstone in the management of HER2-positive breast cancer, improving patient outcomes.

Anti-HER2 agents target HER2 receptors, inhibiting signal transduction pathways and thereby reducing cellular proliferation in HER2-positive breast neoplasms. Currently, utilized agents include trastuzumab, lapatinib, pertuzumab, trastuzumab emtansine (T-DM1), and trastuzumab deruxtecan (T-Dxd). Additionally, neratinib, a recently introduced anti-HER2 drug, may also be employed for the treatment of HER2-positive disease.

In the systemic management of metastatic breast cancer, trastuzumab may be administered in conjunction with pertuzumab and chemotherapy or combined with lapatinib.

In subsequent treatment lines, trastuzumab can be formulated as an antibody-drug conjugate (ADC), such as trastuzumab emtansine or trastuzumab deruxtecan.

Considering adjuvant therapy, trastuzumab can be utilized alongside chemotherapy, particularly taxanes, with or without endocrine therapy, if the carcinoma is hormone-responsive.

The results obtained in patients with advanced disease have provided the rationale for testing the same treatments in earlier stages, where perioperative pharmacological treatments aim to increase the chances of cure. A historical example is the result achieved with the anti-HER2 monoclonal antibody trastuzumab, which, after proving activity in combination with chemotherapy in women with HER2-positive metastatic breast cancer, has also become the standard adjuvant treatment for surgically treated patients with this molecular alteration since 2005 (AIRTUM, 2023). Alongside therapeutic advancements, economic considerations on the utilization of these medications have become increasingly pertinent (Dai et al., 2021).

High prevalence of breast carcinoma and the multifaceted spectrum of treatment modalities, coupled with the distinctive profile of trastuzumab as the inaugural HER-2 targeted therapy integrated into the therapeutic armamentarium for breast carcinoma management, encompassing both early-stage and metastatic scenarios, has steered the investigative spotlight onto this seminal agent (Maadi et al., 2021).

Amidst the myriad conjugated or combinatory formulations pervading the clinical milieu, trastuzumab ADCs are instigating paradigm shifts in the diverse demographic cohorts they cater to. This delineation underscores the pivotal role of trastuzumab and its derivative formulations in reshaping the landscape of breast cancer therapeutics, heralding a new era of precision medicine tailored to the individualised needs of patients.