This is a Phase 3 double-blind study. KS patients are randomized to 1 of 2 treatment arms. They receive either ALRT1057 gel or placebo for 12 weeks. If progressive disease for KS is noted before Week 12, patients are switched to the other blinded treatment arm. If a response or disease progression that has not persisted for at least 4 weeks as of Week 12 occurs, treatment on the blinded arm is continued for up to 4 additional weeks, or until response of disease progression is confirmed. After that time or after 12 weeks of treatment, open-label ALRT1057 may be received.