Autoimmune blistering diseases (AIBDs) can present concurrently with solid or hematologic malignancies. This concomitant finding is believed to be associated with paraneoplastic syndrome, and management typically requires a multidisciplinary approach. This case report describes diagnosis and treatment of a patient previously diagnosed with mucous membrane pemphigoid of the skin who was referred to an oral medicine clinic for evaluation of oral mucosal blisters and gingival bleeding of 8 months' duration. Routine head and neck examination revealed incidental findings of a unilateral large palatine tonsil and fixed submandibular lymph node. A biopsy of the right tonsil was performed, and immunohistochemical analyses revealed markers consistent with mantle cell lymphoma, which was later determined to be stage III. The patient was started on a regimen of acalabrutinib and rituximab. At the 3-month follow-up, the patient's skin and oral blisters had cleared, and she was completely asymptomatic. To ensure timely referral and better patient outcomes, careful attention should be paid to subtle cues that can lead to early detection of malignancies in persons with AIBDs.