This invention relates to the diagnosis and treatment of cancerous diseases, particularly to the mediation of cytotoxicity of tumour cells evidencing surface expression of CD44; and most particularly to the use of cancerous disease modifying antibodies (CDMAB), optionally in combination with one or more chemotherapeutic agents, as a means for initiating the cytotoxic response. The invention further relates to binding assays which utilize the CDMAB of the instant invention.