Patients receive standard high-dose IL-2 therapy, with an opportunity to crossover to the experimental arm if there is disease progression noted after two cycles of high-dose IL-2. Crossover patients will be included in Arm A.

Patients will receive two doses of radiation before receiving high-dose IL-2.

Patients 1 - 20 will receive a single fraction of radiation. Patients 21 through the completion of the study will receive two fractions. The dose for all patients will be 20 Gy per fraction to the prescription line at the edge of the planning treatment volume (PTV) with the last dose delivered on a Friday before IL-2 administration. For patients receiving two radiation doses, the doses can be administered on the Wednesday and Friday before IL-2 starts. Patients who are assigned to IL-2 monotherapy and have progressive disease after two IL-2 cycles are then eligible to receive SBRT before cycle 3 of IL-2 commences, single fraction for patients 1-20 and two fractions for patients 21- end of study.

Determine the best overall tumor response rate of high dose IL-2 versus SBRT + high-dose IL-2 using RECIST v1.1 assessed by CT/MRI, criteria applied to all target and non-target lesions with the exclusion of sites treated with SBRT. For patients who have SBRT after progression on IL-2 monotherapy, the response rate will be recorded, but not counted as a response for the primary objective.

Overall response rate (ORR) includes all measurable and non-measurable target lesions except the lesions treated by SBRT, which were assessed separately. Both CT and positron emission tomography imaging were employed to assess response.

Complete Response: disappearance of all target/non-target lesions and no abnormalities on PET; Partial Response: ≥30% decrease in sum of longest diameter (LD) of target lesions; Progressive Disease: ≥20% increase in sum of LD recorded since tx start or appearance of ≥1 new lesions; Stable Disease: Neither qualifying for PR nor PD since tx started.

Measure the response rate of patients who have disease progression after the first IL-2 cycles (using RECIST criteria) who received SBRT prior to cycle 3 of IL-2.

Patients receive standard high-dose IL-2 therapy, with an opportunity to crossover to the experimental arm if there is disease progression noted after two cycles of high-dose IL-2. Crossover patients will be included in Arm A.

High-dose IL-2: IL-2 will be given on a Monday at a dose of 600,000 IU per kilogram IV every 8 hours for up to 14 doses each cycle. The second cycle is planned 16 days after cycle 1 but may be delayed up to one week to allow toxicity to resolve. The maximum number of doses that can be given during two cycles will be 28 doses. Patients who respond after two cycles can receive 4 more cycles of IL-2. Patients with disease progression after 2 cycles may elect to receive radiation before a 3rd cycle of IL-2. If patients crossover, IL-2 will be given on the Monday following the last dose of radiation, at a dose of 600,000 IU per kilogram IV every 8 hours for a maximum of 14 doses each cycle. Another cycle is planned 16 days after cycle 3 but may be delayed up to one week to allow toxicity to resolve.

Determine the best overall tumor response rate of high dose IL-2 versus SBRT + high-dose IL-2 using RECIST v1.1 assessed by CT/MRI, criteria applied to all target and non-target lesions with the exclusion of sites treated with SBRT. For patients who have SBRT after progression on IL-2 monotherapy, the response rate will be recorded, but not counted as a response for the primary objective.

Overall response rate (ORR) includes all measurable and non-measurable target lesions except the lesions treated by SBRT, which were assessed separately. Both CT and positron emission tomography imaging were employed to assess response.

Complete Response: disappearance of all target/non-target lesions and no abnormalities on PET; Partial Response: ≥30% decrease in sum of longest diameter (LD) of target lesions; Progressive Disease: ≥20% increase in sum of LD recorded since tx start or appearance of ≥1 new lesions; Stable Disease: Neither qualifying for PR nor PD since tx started.

There will be a comparison of the overall tumor response of patients receiving one versus two SBRT doses. Responses from patients who participated in the crossover portion of the study were excluded.

Patients receive standard high-dose IL-2 therapy, with an opportunity to crossover to the experimental arm if there is disease progression noted after two cycles of high-dose IL-2. Crossover patients will be included in Arm A.

High-dose IL-2: IL-2 will be given on a Monday at a dose of 600,000 IU per kilogram IV every 8 hours for up to 14 doses each cycle. The second cycle is planned 16 days after cycle 1 but may be delayed up to one week to allow toxicity to resolve. The maximum number of doses that can be given during two cycles will be 28 doses. Patients who respond after two cycles can receive 4 more cycles of IL-2. Patients with disease progression after 2 cycles may elect to receive radiation before a 3rd cycle of IL-2. If patients crossover, IL-2 will be given on the Monday following the last dose of radiation, at a dose of 600,000 IU per kilogram IV every 8 hours for a maximum of 14 doses each cycle. Another cycle is planned 16 days after cycle 3 but may be delayed up to one week to allow toxicity to resolve.