Li, H. et al.

Osseous sarcoidosis mimicking metastatic breast cancer.

CMAJ 2020 July 13;192:E799-802. doi: 10.1503/cmaj.191661

Breast cancer is the most common cancer with 1 in 8 women diagnosed during their lifetime. Early stage breast cancer, which is the most common, is treated with the plan for a cure. Often breast cancer treatment will involve surgery, adjuvant chemotherapy, radiation, and endocrine therapy. While less common in presentation, metastatic breast cancer is incurable with a 5-year survival of only 27.4%. Treatment of metastatic breast cancer typically involves lifelong chemotherapy or endocrine therapy, which entails significant potential morbidity. Therefore, accurate staging and diagnosis of metastatic disease is essential.

While metastasis from breast cancer can occur many places in the body, bone is the most common site, accounting for 65-75% of metastatic breast cancer patients. Bone metastasis is often characterized on imaging such as magnetic resonance imaging (MRI). On imaging such as MRI, it can be difficult to assess for true metastatic lesions versus alternative diagnoses. Bone metastases from breast cancer are typically lytic, meaning that there is area of bone destruction at the site of metastasis. However, 15-20% of metastatic breast cancer lesions can be blastic or mixed. Some non-cancerous processes can appear similar to metastatic disease to the bone on imaging and MRI. It is therefore essential to ensure true diagnosis of metastatic lesions especially given the poor prognosis and morbidity associated with metastatic breast cancer treatment.

One disease process that can mimic metastatic breast cancer is sarcoidosis. Sarcoidosis is a multisystem granulomatous disease. Sarcoidosis usually begins in the lungs; however, any organ can be affected. The cause of sarcoidosis is unknown but thought to be related to an immune reaction. Most sarcoidosis resolves without intervention in a few years, but some require medications such as anti-inflammatory drugs. Sarcoidosis involves bone in 3-13% of cases. Similar to bone metastasis in breast cancer, sarcoidosis of the bone also has a lytic appearance on imaging.

While sarcoidosis of the bone is rare and encountered less frequently than skeletal metastasis, it is important to keep on the list of potential diagnoses for a patient with breast cancer and bone lesions. Given similar imaging and vastly different prognosis and treatment, sarcoidosis should be kept on the differential and evaluated in the diagnostic workup. If there is lack of clarity on diagnostic imaging, then a biopsy to obtain a tissue diagnosis is recommended.