The numb chin in breast cancer.

Numbness of the chin, an uncommon neurological symptom, was observed in 15 patients with cancer. Thirteen had breast cancer. This symptom usually heralded progressive involvement of the cranial nerves or cerebrum and denoted a poor prognosis in patients with a short `tumourfree interval'. The pathogenesis is commonly related to dural involvement of the Vth cranial nerve at the base of the brain, although metastasis to the mandible might sometimes be implicated. The reason for the peculiar predilection for the mandibular branch of the trigeminal nerve to be affected by breast cancer is not known.