Cutaneous T-cell lymphoma (CTCL) is a malignancy of skin-homing T cells associated with increased risk of second malignancies. CAR-T lymphoma is a mature T-cell malignancy arising in cancer patients treated with chimeric antigen receptor T-cell (CAR-T) therapy. Because of its frequent cutaneous involvement, CAR-T lymphoma can mimic CTCL, which in turn can resemble cutaneous sequelae of oncologic therapies. Careful evaluation of these entities in cancer patients is therefore essential, yet little guidance exists regarding optimal methods of screening, diagnosis, and treatment. Clinicians managing CTCL in cancer patients should consider how oncologic treatment toxicities may overlap with CTCL treatment toxicities or affect patients’ risk for other skin cancers. Where possible, immune-boosting or at least immune-preserving treatments are preferred, with immune checkpoint inhibition emerging as an important option in selected patients. Patients with a history of CAR-T therapy and new, persistent skin findings should undergo careful work-up with molecular screening for lymphoproliferative processes. Presence of a CAR in lesional tissue can be suggestive but is not diagnostic of a CAR-T-associated malignancy. Treatment for any patient with a cutaneous T-cell or CAR-T lymphoma and a second cancer should be an interdisciplinary effort tailored to the patient’s specific medical history and molecular profile. Further research is needed to establish better evidence-based guidelines for treatment of these patient populations.