Management and Mechanisms of Diarrhea Induced by Tyrosine Kinase Inhibitors in Human Epidermal Growth Factor Receptor-2-Positive Breast Cancer

Breast cancer has the highest incidence among female malignancies, significantly impacting women's health. Recently, numerous HER2-targeted therapies have achieved excellent clinical outcomes. Currently, anti-HER2 drugs are divided into three main categories: monoclonal antibodies, small-molecule tyrosine kinase inhibitors, and antibody-coupled drugs (ADCs). The main toxic side effects of small molecule TKI-based therapy are diarrhea, hand-foot syndrome, rash, nausea, and vomiting. Diarrhea is a potential predictor of tumor response, affecting up to 95% of cancer patients treated with TKIs. Severe gastrointestinal toxicity can result in the need for dose reductions and treatment interruptions. This not only compromises the efficacy of TKIs but also deteriorates human nutrition and quality of life. The majority of individuals develop diarrhea within 7 days of starting treatment, with approximately 30% developing grade 3 or higher diarrhea within 2-3 days of starting treatment. The severity of diarrhea typically correlates with the dosage of most TKIs. Current prevention and management strategies are primarily empirical, focusing on symptom alleviation rather than addressing the toxicological mechanisms underlying TKI-induced diarrhea. Consequently, anti-diarrheal drugs are often less effective in managing this condition in cancer patients receiving TKIs. Moreover, our understanding of the toxicological mechanisms responsible for such diarrhea remains limited, underscoring the urgent need to identify these mechanisms in order to develop effective anti-diarrheal medications tailored to this specific context. This review aims to elucidate management approaches and mechanisms for diarrhea induced by TKIs during HER2-positive breast cance. Breast cancer has the highest incidence among female malignancies, significantly impacting women's health. In recent years, numerous HER2-targeted therapies have been developed, including lapatinib, neratinib, tucatinib, and pyrotinib. However, second-generation tyrosine kinase inhibitors (TKIs) often cause severe gastrointestinal toxicity, necessitating dose reduction and treatment interruption. This not only compromises the efficacy of TKIs but also deteriorates nutritional status and quality of life. Diarrhea is a potential predictor of tumor response and is the second most common adverse event, affecting up to 95% of cancer patients treated with TKIs. Approximately 30% of these patients experience grade 3 or higher diarrhea within just 2-3 days of initiating TKI treatment. The severity of diarrhea typically correlates with the dosage of most TKIs. Current prevention and management strategies are primarily empirical, focusing on symptom alleviation rather than addressing the toxicological mechanisms underlying TKI-induced diarrhea. Consequently, anti-diarrheal drugs are often less effective in managing this condition in cancer patients receiving TKIs. Moreover, our understanding of the toxicological mechanisms responsible for such diarrhea remains limited, underscoring the urgent need to identify these mechanisms to develop effective antidiarrheal medications tailored for this specific context. This review aims to elucidate management approaches for diarrhea induced by HER2 tyrosine kinase inhibitors during breast cancer treatment.