Pitfalls on image evaluation of tumor viability and anti-tumor efficacy in metastatic mucinous breast cancer: A case report.

A 66-year-old woman with metastatic mucinous breast cancer was referred to our hospital. The patient had lymph node and multiple lung metastases judged as progressive disease. Positron emission tomography showed radio tracer uptake neither in the axillary lymph nodes nor in the lung metastases. Chemotherapy brought about marked regression of the lymph node and lung metastases. Pathological study of the regressed but still swollen metastatic axillary lymph nodes showed no viable cancer cells with fibrosis and abundant mucin. Multidisciplinary treatment including chemotherapy followed by endocrine therapy fortunately resulted in complete response of the lung lesions. The patient has been well on endocrine therapy for more than 3 years without any image detectable cancer foci. Diagnostic physicians should note that the presence of mucin in mucinous breast cancers can cause underestimation of tumor viability assessment with positron emission tomography and therapeutic efficacy assessment with various image modalities.