The mesylate salt form of larotinib, a reversible pan-ErbB inhibitor with potential antineoplastic activity. Upon administration, larotinib binds to and inhibits ErbB tyrosine receptor kinases, which may result in the inhibition of cellular proliferation and angiogenesis in tumors expressing ErbB. The ErbB protein family, also called the epidermal growth factor receptor (EGFR) family, plays major roles in tumor cell proliferation and tumor vascularization.