Association between CA 15‑3 and progression of interstitial lung disease in a case of coexisting systemic sclerosis and recurrent breast cancer: A case report.

Carbohydrate antigen 15-3 (CA 15-3) is known as a specific tumor marker for breast cancer, the main use of which is monitoring therapy in patients with advanced breast cancer. Either systemic sclerosis (SSc)-interstitial lung disease (ILD) or pulmonary arterial hypertension is currently the leading cause of disease-related morbidity and mortality in patients with scleroderma. Although CA 15-3 has been investigated as a biomarker in SSc-ILD, its role remains unclear. The current report presented a case of recurrent breast cancer diagnosed with SSc-ILD during treatment. The patient, at 63 years old, experienced shortness of breath with minimal exertion after four cycles of perutuzumab, trastuzumab and weekly paclitaxel. Computed tomography (CT) revealed ground-glass opacities and linear shadows in the peripheral lower lobes of both lungs. Although the development of lung involvement associated with breast cancer, such as carcinomatous lymphangitis, was initially suspected, because of the increase in CA 15-3, skin biopsies were taken from the left index finger base and extension side of the left elbow, which demonstrated increased thickness of the dermis, leading to a diagnosis of SSc-ILD. The findings in this case suggested the importance of considering a differential diagnosis, including ILD, concurrently while screening for the progression of recurrent breast cancer when encountering patients with breast cancer and elevated levels of CA 15-3.