A 59-year-old female patient presented a painful expansive tumor in the mandible, with 3 months of evolution. Computed tomography revealed a hypodense, unilocular lesion, with ill-defined limits and a moth-eaten appearance, with expansion and disruption of the cortical bone, measuring 30 mm, located on the right side of the mandibular body, extending close to the base of the mandible. Medical history was not contributory. An incisional biopsy was performed. Microscopic examination revealed proliferation of neoplastic cells arranged in nests, trabeculae, and duct-like structures. The cells had a cuboidal and polyhedral shape, eosinophilic cytoplasm, hyperchromatic and pleomorphic nuclei, and loss of cell cohesion. Neoplastic nests surrounding irregular bone trabeculae were observed. Neoplastic cells were immunopositive for AE1/AE3, CK7, and Ki67 (40%). Negativity was observed for CD31, CD34, factor VIII, CD99, S100, and CK20. The final diagnosis was metastatic adenocarcinoma, and the patient was referred for further treatment. Funding: CAPES. A 59-year-old female patient presented a painful expansive tumor in the mandible, with 3 months of evolution. Computed tomography revealed a hypodense, unilocular lesion, with ill-defined limits and a moth-eaten appearance, with expansion and disruption of the cortical bone, measuring 30 mm, located on the right side of the mandibular body, extending close to the base of the mandible. Medical history was not contributory. An incisional biopsy was performed. Microscopic examination revealed proliferation of neoplastic cells arranged in nests, trabeculae, and duct-like structures. The cells had a cuboidal and polyhedral shape, eosinophilic cytoplasm, hyperchromatic and pleomorphic nuclei, and loss of cell cohesion. Neoplastic nests surrounding irregular bone trabeculae were observed. Neoplastic cells were immunopositive for AE1/AE3, CK7, and Ki67 (40%). Negativity was observed for CD31, CD34, factor VIII, CD99, S100, and CK20. The final diagnosis was metastatic adenocarcinoma, and the patient was referred for further treatment. Funding: CAPES.