A 70-year-old man presented with malaise, heartburn, and sudden eruption of multiple seborrheic keratoses on the back (Fig. 1). Upper gastrointestinal endoscopy disclosed a poorly differentiated adenocarcinoma with infiltration through the serous membrane and duodenal involvement. Gastrectomy, nodal dissection, and gastro-jejunal anastomosis were performed. Eruptive seborrheic keratoses are rather uncommon and usually inflammatory in nature. However, this phenomenon is also named as the sign of Leser-Trélat and may herald internal malignancies such as gastrointestinal adenocarcinoma, colon cancer, breast cancer, and lung cancer. Although the sign of Leser-Trélat is debated because of the common occurrence of seborrheic keratoses in older patients, there are reports of young patients showing this phenomenon with underlying cancer. The sudden appearance of seborrheic keratoses is thought to be associated with various cytokines and growth factors produced by the underlying neoplasm. This clinical image highlights the importance of considering internal malignancy in the differential diagnosis of patients presenting with eruptive seborrheic keratoses.