Occult lobular breast cancer first discovered through colon metastases

What happened, in summary

A 73-year-old woman with chronic watery diarrhoea came to hospital with worsening abdominal symptoms, confusion, low blood pressure, and hypoglycaemia. Colonoscopy was performed after infectious stool studies were negative. Several polyps were benign tubular adenomas, but random biopsies from the colonic mucosa showed malignant cells consistent with metastatic invasive lobular breast carcinoma. The cells were oestrogen-receptor positive, progesterone-receptor negative, HER2 negative, and E-cadherin negative, supporting a breast lobular origin rather than a primary colorectal cancer. Her CA 27.29 tumour marker was elevated at 188. Mammography and breast ultrasound showed dense tissue but no identifiable primary breast lesion, and further breast MRI was not pursued because it would not change systemic treatment. The cancer was therefore managed as occult metastatic breast cancer presenting in the colon. She started letrozole and palbociclib. During follow-up, CA 27.29 fluctuated near baseline before falling to 136. Her course was complicated by repeated urinary tract infections and one admission for C. difficile colitis after antibiotics. Palbociclib had to be held several times during these acute illnesses. Imaging and tumour-marker monitoring continued to assess disease burden. Two years after the diagnosis, she developed urosepsis and died. Her case illustrates how lobular breast cancer can first appear through gastrointestinal metastases even when breast imaging does not reveal a primary tumour.