It has been discovered that As.sub.2O.sub.3 suppresses tyrosine kinase receptors, in particular EGFR and IL-6R, by targeting RTKs to lysosomes and/or proteasome for degradation. This is the basis for the discovery that cancers dependent on RTKs for signaling, proliferation, survival, metastasis and differentiation can be treated with As.sub.2O.sub.3, preferably oral As.sub.2O.sub.3. Representative cancers include EGFR and cytokine dependent cancers, for example, head and neck squamous sarcomas and multiple myelomas, respectively.