AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.
Inclusion Criteria:
* Confirmed mycosis fungoides/Sezary syndrome, disease stage IB (defined as patches, plaque, or papules that involve 10% of the skin surface viscera) or higher.
* Age ≥ 18 years.
* ECOG Performance Score between 0-1
* Receipt of at least one prior systemic therapy for MF/SS.
* Previous systemic anti-cancer therapy must have been discontinued at least 2 weeks prior to treatment. See section 6.2 Subject Exclusion Criteria for guidelines regarding adjuvant and maintenance therapy for prior malignancy.
* Topical or systemic steroids (equivalent to ≤ 10 mg/day of prednisone) may be considered if dose has been constant and discontinuation may lead to rebound flare in disease, adrenal insufficiency, and/or unnecessary suffering.
* Prior therapy with gemcitabine allowed.
* Refer to Table 1 for laboratory inclusion criteria.
* The participant (or legally acceptable representative if applicable) provides written informed consent for the trial.
* A female participant is eligible to participate if she is not pregnant, not breastfeeding, and at least one of the following conditions applies:
* Not a woman of childbearing potential (WOCBP) as defined in Appendix C
* A WOCBP who agrees to follow the contraceptive guidance in Appendix C
* A male participant must agree to use a contraception as detailed in Appendix C of this protocol from screening and through 6 months after the last dose of gemcitabine or 120 days after the last dose of pembrolizumab (whichever is la…