EGFR-Mutated Lung Adenocarcinoma Presenting as Miliary Intrapulmonary Carcinomatosis: A Diagnostic Mimic of Tuberculosis

Miliary intrapulmonary carcinomatosis (MIPC) is a rare metastatic pattern of lung cancer that closely mimics disseminated tuberculosis (TB), posing a significant diagnostic challenge. We present a 53-year-old Filipino woman, a lifelong nonsmoker with prior latent TB, who presented with progressive cough and a diffuse bilateral miliary nodular pattern on chest imaging. An extensive infectious workup was unrevealing, and bronchoscopic biopsy revealed poorly differentiated adenocarcinoma (TTF-1+) harboring an EGFR exon 21 L858R mutation. Staging demonstrated brain, osseous, and pleural metastases (stage IVB NSCLC). The patient was initiated on osimertinib 80 mg daily with palliative radiation and zoledronic acid, achieving no evidence of active disease at 2.5 years on serial PET-CT and brain MRI. This case underscores the importance of tissue diagnosis in unresolved miliary patterns, early molecular profiling in lung adenocarcinoma, and the potential for durable exceptional responses with osimertinib in EGFR-mutated NSCLC.