What happened, in summary

A 61-year-old nonsmoking woman was diagnosed in February 2017 with Stage IV lung adenocarcinoma carrying both EGFR L858R and T790M mutations. She started gefitinib at another institution, but within a few months her cancer clearly progressed with a miliary pattern of pulmonary metastases.

In September 2017, treatment was changed to osimertinib. Her shortness of breath improved substantially. After 3 months, CT imaging showed new bilateral ground-glass opacities, raising concern for drug-induced pneumonitis. At the same time, however, the miliary metastatic pattern had improved markedly and she continued to feel better.

Because she remained clinically stable and her dyspnea was improving, the team considered the lung opacities more consistent with lymphangitic cancer responding to treatment than with symptomatic drug toxicity. Osimertinib was therefore continued at 80 mg daily without adding steroids.

Over the next year, repeated imaging showed an excellent tumour response and gradual improvement in the ground-glass changes. Her course highlighted the importance of interpreting new lung findings alongside symptoms and overall cancer response, since stopping an effective targeted therapy for presumed pneumonitis could have changed her treatment unnecessarily.