MET-Positive Metastatic Lung Cancer That First Appeared as a Breast Mass

What happened, in summary

A 74-year-old woman presented with a rapidly growing left breast mass, major weight loss, fatigue, and night sweats. Breast biopsy initially suggested a poorly differentiated triple-negative breast cancer, but the pathology was not definitive. PET-CT then showed a dominant left lung abnormality, pulmonary nodules, thoracic lymphadenopathy, and other disease sites.

Additional testing changed the diagnosis. The breast tumor was TTF-1 positive, and genomic testing found a MET exon 14 skipping mutation, supporting metastatic lung adenocarcinoma rather than a primary breast cancer. Staging showed spread to the breast, liver, and later the right adrenal gland, making this Stage IV lung cancer.

She received palliative radiation to the painful breast metastasis and started capmatinib. After 3 months, scans showed a marked reduction in disease burden. At about 6 months, however, the right adrenal metastasis enlarged while the other sites continued to respond. New MET resistance mutations were detected. Surgery to remove the adrenal lesion was attempted but could not be completed because of its extent. Palliative radiation and second-line systemic treatment were being considered.