Case Presentation: A 78 year old male with a history of atrial fibrillation, type 2 diabetes and former significant tobacco use, presented with a one month history of left sided neck pain. The pain was progressive and he subsequently developed left upper extremity swelling along with a rash involving the neck, left anterior chest and back. In the hospital, the patient reported no recent infections or travels, fevers, dyspnea, or weight changes. On physical exam, patient was noted to have a firm, indurated mass on his left upper back along with a vesicular rash in a T3-4 dermatomal pattern concerning for shingles. Laboratory findings were significant for leukocytosis, normal calcium level and HIV was negative. Ultrasound confirmed a thrombus in the left internal jugular vein along with left cervical, supraclavicular and axillary lymphadenopathy, and he was started on Lovenox for anticoagulation. Due to the unknown cause of the hypercoagulability, a CT Chest was performed which revealed a right upper lobe heterogenous enhancing mass concerning for malignancy. A skin biopsy was subsequently performed which revealed primary adenocarcinoma of the lung. Immunohistochemical staining was positive for TTF-1, a marker that is sensitive and specific for primary adenocarcinoma, as well as PD-L1, CK20 and KRAS mutation.

Discussion: Lung cancer is both the second most common malignancy and the leading cause of cancer-associated mortality. It typically metastasizes to the brain, bone, liver and adrenal glands. In rare cases, however, lung cancer may metastasize to the skin and has been reported in 1-12% of lung cancer cases. Here we present a case of skin metastases in zosteriform pattern from a primary lung adenocarcinoma. Overall, in men who present with skin metastases, the most common primary site is lung cancer. Furthermore, 20-60% of skin metastasis from lung cancer cases present initially with cutaneous findings before diagnosis of primary lung cancer is made. Commonly, skin metastases are seen on the chest, back and neck but usually are not distributed in a dermatome area. In our case, the possible pathogenesis of the zosteriform skin metastasis may have been due may be due to emboli from the cancer that causes lymphatic congestion and blockage.  This could then lead to the skin lesions and left upper extremity swelling as seen in this patient.

Conclusions: This case highlights the importance of recognizing new skin findings in high risk patients such as those with significant smoking history as one of the first clinical manifestation of a possible occult malignancy.