Enlargement of a Preexisting Pulmonary Nodule Mimicking Metastasis during Neoadjuvant Chemotherapy with Pembrolizumab for Triple-Negative Breast Cancer.

INTRODUCTION

Neoadjuvant immunochemotherapy with immune checkpoint inhibitors (ICIs) can yield atypical radiological patterns that may complicate response assessment and management decisions in curative-intent settings.

CASE PRESENTATION: A 50-year-old female with triple-negative breast cancer received neoadjuvant chemotherapy with pembrolizumab. While the primary breast tumor showed marked regression, a preexisting subpleural pulmonary nodule gradually enlarged over 6 months without respiratory symptoms or fluorodeoxyglucose uptake on PET-CT. As metastatic disease could not be excluded based on imaging alone, video-assisted thoracoscopic resection was performed. Histopathology revealed lymphocyte-predominant inflammation with hemosiderin-laden macrophages and no histological evidence of malignancy, consistent with a benign inflammatory lesion. The final pathological diagnosis was inflammatory change arising within a preexisting pulmonary bulla. The patient showed no signs of recurrence on follow-up imaging performed 1 year after breast surgery.

CONCLUSIONS

Discordant enlargement of a solitary pulmonary nodule during ICI-based therapy requires serial imaging and awareness of PET limitations for small nodules. When feasible, tissue confirmation may prevent premature abandonment of curative-intent treatment.