Metastatic Adenocarcinoma of the Lung Presenting as a Soft Tissue Mass

Abstract

Lung cancer is the leading cause of cancer death in the United States, with more than 230,000 new cases, and approximately 150,000 deaths estimated for 2018. Lung cancer most commonly metastasizes to the brain, liver, lungs, bone, and adrenal system; however, there have been several cases of spread to soft tissues, with an incidence rate of approximately 0.75-9%. The objective of this case report is to highlight an unusual presentation of metastatic adenocarcinoma of the lung. In this case report, patient presented with a $3\times 3$  cm soft tissue mass on the back. The mass was slowly growing but had become more painful and wished to have it excised. Preoperatively, the mass was suspected to be a sebaceous cyst but intraoperatively had deep attachments and other suspicious findings. Pathology had a positive immunoprofile for metastatic adenocarcinoma favoring a lung primary. Given this presentation of metastases, the prognosis is poor with a survival time decreasing to around 5 months. Overall, this case reinforces the importance of sending all soft tissue masses for final pathology with accurate labeling and the importance of immunohistochemical testing in aiding the identification of the primary.