<s>[INST] Mom, just got diagnosed with brain cancer with a 1 inch by 1 inch tumor in her head. She has just finished up with breast cancer, surgery, mastectomy and radiation last month. About 2 weeks ago she started losing her balance and not thinking straight. Her breast cancer was stage 3 and in lymph nodes which were removed. [/INST] Thanks for your question on Chat Doctor. Breast cancer is very notorious in spread. And brain metastases are very common. So even with the absence of brain metastases it is protocol to give prophylactic radiotherapy to brain for prevention of brain metastases. But your mother already had brain Mets, so chances of worsening brain Mets are more at present. Imbalance mostly due to this only. So get done repeat MRI brain for this. Another possibility is cerebral edema due to tumor and radiation. MRI brain will also diagnose this. So get done MRI Brain and consult your oncologist to rule out worsening brain metastases. </s>