Double Primary Malignancies Involving Cutaneous Carcinoma

Multiple primary malignancies (MPMs) refer to the presence of 2 or more histologically distinct malignant tumors in the same individual. The prevalence of MPMs has increased owing to earlier detection of tumors by screening tests and improved treatment modalities for primary tumors. Although any combination of malignant tumors is possible, reports of MPMs involving cutaneous carcinoma are uncommon in the literature. Herein, we present 2 uncommon cases of synchronous double primary malignancies involving basal cell carcinoma and primary cutaneous mucinous carcinoma as the index tumors, accompanied by a thyroid carcinoma and a thymoma as the second malignancy, respectively. The authors also describe the usefulness of positron emission tomography/computed tomography for detecting occult primary tumors in patients with cutaneous malignancies.