An evolving pathology: colorectal cancer with metastasis to the axilla; the treatment approach and response

Colon adenocarcinoma is a well-studied surgical pathology with a streamlined treatment regimen. The typical areas of disease metastasis include liver and lungs, however, there have been reports of unusual locations of disease spread. This includes metastases to the breast, thyroid and testes, which often lead to deferral from conventional treatments. An 83-year-old female presented to her general practitioner with dizziness, fatigue, and altered bowel motions. Subsequently, a surgeon is confronted with this case of mucinous adenocarcinoma with axillary metastasis, diagnosed by FluoroDeoxyGlucose (FDG) Positron Emission Tomography (PET) with Computed Tomography (CT) and confirmed with biopsy. Her tumour was found to be both microsatellite instability/mismatch repair (MSI/MMR) deficient and KRAS A146V positive. How should this influence treatment? We discuss this pathology, its treatment implications, as well as a brief literature review. This is the first case of metastatic colorectal cancer to the axilla in Australia and the only reported of such cases in literature with both MSI/MMR deficiency and KRAS146V mutation.