Eribulin mesylate is primarily used in the treatment of metastatic breast cancer, particularly for patients who have previously undergone at least two chemotherapy regimens. It works by inhibiting the growth phase of microtubules, which are essential for cell division, thereby slowing or stopping the proliferation of cancer cells. This makes it a valuable option for managing advanced stages of the disease where other treatments have failed. Additionally, it has shown efficacy in treating liposarcoma, a rare type of soft tissue sarcoma, offering an alternative for patients with limited therapeutic options. Its ability to improve overall survival rates in these conditions underscores its importance in oncology.