ALK-Rearranged NSCLC With Concomitant HER2-Mutant Breast Cancer Patient Treated With Alectinib, Trastuzumab, and Pertuzumab: A Case Report

Multiple cancers are a common occurrence, and the choice of treatment can be a challenging decision. The current case report describes a 71-year-old woman with overlapping anaplastic lymphoma kinase (ALK)-rearranged lung adenocarcinoma and HER2-mutant breast cancer, who achieved improvement with concurrent use of the molecularly targeted agents Alectinib, Trastuzumab, and Pertuzumab. A 71-year-old woman was diagnosed with lung adenocarcinoma and brain metastases, and invasive ductal carcinoma of the right breast, HER2-mutant type. In March 2021, a biopsy confirmed the presence of the ALK fusion gene in lung cancer. In April 2021, he started Alectinib and showed shrinkage of lung cancer; in December 2021, a metastatic liver tumor was found, and a liver biopsy diagnosed liver metastasis of breast cancer. Therefore, Alectinib was discontinued in February 2022, and Trastuzumab, Pertuzumab, and Docetaxel were started as chemotherapy for breast cancer. She continued treatment with Trastuzumab and Pertuzumab, but in July 2022, she developed an increase in lung cancer. Her metastatic liver tumor continued shrinking, and she was started on Trastuzumab, Pertuzumab, and Alectinib. After six months of treatment, the patient showed a sustained reduction in both lung cancer, breast cancer, and brain metastases with no adverse events. ALK rearrangement lung cancer often develops in young women, and similarly, breast cancer often develops in women. Therefore, those cancers may occur simultaneously. In such cases, the choice of treatment can be difficult, as both cancers require different approaches. Alectinib has been shown to have a high response rate and prolonged progression-free survival in ALK-rearranged non-small cell lung cancer (NSCLC). Trastuzumab and Pertuzumab are commonly used for the treatment of HER2-mutant breast cancer and have been shown to significantly improve progression-free survival and overall survival. This case report provides evidence that the concurrent use of Alectinib, Trastuzumab, and Pertuzumab can be an effective treatment for patients with overlapping ALK-rearranged NSCLC and HER2-mutant breast cancer. It is important to consider concurrent treatment in patients with multiple cancers to optimize treatment outcomes and improve quality of life. However, further studies are needed to establish the safety and efficacy of this combination of drugs for the treatment of overlapping cancers.