PORT is a multicentre, single arm, phase II trial of pembrolizumab in combination with radiotherapy for patients with relapsed/refractory CTCL.

All registered patients will receive a single IV infusion of pembrolizumab (200mg) given at 3 weekly intervals. At 12 weeks patients will start radiotherapy at a dose of 12Gy in 3 fractions. Patients who progress on pembrolizumab before week 12 will start radiotherapy as soon as possible after progression.  Following completion of radiotherapy, patients will continue pembrolizumab on the same schedule until disease progression or the development of unacceptable toxicity or for a maximum of 2 years, whichever comes earlier.

Patients must be at least 18 years of age with relapsed, refractory or progressed stage IB-IVB CTCL mycosis fungoides/Sézary Syndrome. They must have at least 1 cutaneous lesion suitable for palliative radiotherapy and at least 1 measurable lesion with a minimum mSWAT score of 10, or 2 or more cutaneous tumours which will not be irradiated but must be measurable.  Patients must have an ECOG performance status of 0-1 and adequate organ function.  Patients cannot have received chemotherapy,targeted small molecule therapy, other monoclonal antibody, prior treatment with anti-PD-1, anti-PD-L1, anti-PD-L2 therapy or IMP within 4 weeks prior to the first dose of pembrolizumab.  They cannot have CNS involvement, active autoimmune disease requiring systemic treatment in the past 2 years, a history of active TB or received a live vaccine within 30 days prior to the first dose of pembrolizumab.