Hemorrhagic Brain Metastases in a Patient with Anaplastic Lymphoma Kinase (ALK)-Rearranged Invasive Mucinous Adenocarcinoma of the Lung.

BACKGROUND Invasive mucinous adenocarcinoma (IMA) is a rare variant of adenocarcinoma of the lung. It frequently shows KRAS mutations, while ALK rearrangement is exceedingly rare. We present a case of ALK-rearranged IMA of the lung presenting with an unusual pattern of brain metastases, radiologically mimicking a cavernous angioma. CASE REPORT A 44-year-old non-smoker female was first diagnosed with lung right lower lobe IMA with ALK rearrangement. Five years after surgery followed by chemotherapy, she developed a sudden onset headache. Brain imaging revealed a hemorrhagic left frontal mass, suspicious for a cavernous angioma. However, the pathology of the resected lesion showed an ALK-rearranged brain metastasis from the IMA of the lung. Interestingly, the metastases showed perivascular tumor infiltrates, accompanied by focal mural invasion, vascular disruption, and hemorrhage. CONCLUSIONS To our knowledge, this is the first reported case of brain metastasis from an ALK-rearranged IMA of the lung. Further investigation of the clinical and pathological characteristics of the ALK-rearranged IMA, including awareness of the possibility for development of brain metastases with tumor-associated vasculopathy and hemorrhage, is warranted.