Leptomeningeal carcinomatosis as initial presentation in adenocarcinoma of lung with signet ring cell features: an autopsy case report.

Signet ring cell (SRC) features are rare but well-recognized cytological changes of pulmonary adenocarcinoma (PA). PA with SRC features (PA-SRC) is frequently associated with anaplastic lymphoma kinase (ALK) gene rearrangement, and recognition of PA-SRC may be important for the administration of targeted treatment. To the authors' knowledge, leptomeningeal carcinomatosis (LMC) as an initial presentation of PA-SRC has not yet been reported. We report an autopsy case from a 59-year-old female who presented with intractable headache for 6 weeks and died of LMC as a result of metastatic PA-SRC. Premortem brain MRI showed nonspecific leptomeningeal enhancement. At autopsy, a tan rubbery mass was found in the hilar area of the right lung, which also surrounded the lower trachea and carotid arteries. A right posteromedial middle lobe mass was also found. Leptomeninges were slightly thickened, without discrete masses. Microscopic examination of the lung mass and leptomeninges showed solid sheets and nests of malignant cells with pleomorphic nuclei and frequent SRC features which comprised 50% of the mass. Immunohistochemically, the tumor cells demonstrated strong diffuse expression of cytokeratin (CK)-7, TTF-1, and napsin-A. Immunostains for CK-20 and ALK were negative. These features were consistent with PA-SRC. It has been reported that approximately 70% of PAs demonstrate ALK gene rearrangement when SRCs comprised >10% of the tumor cells. The presence of SRCs can be indicative of a lung primary and, because of frequent ALK gene rearrangement in PA-SRC, proper recognition of PA-SRC may be important in determining whether further testing is advisable (e.g., ALK immunostaining and/or ALK gene rearrangement).