Yes: Merrick I. Ross, MD, The University of Texas MD Anderson Cancer Center, Houston, Texas
No: Robert Andtbacka, MD, Hunstman Cancer Institute at the University of Utah, Salt Lake City, Utah
Dr. Ross outlined the spectrum of intralesional therapy targets, including 1) stage IIIB/C regionally metastatic in-transit disease with or without nodal disease; 2) stage M1a (distant skin, soft tissue, and nodal metastases); and 3) the second situation with low-volume visceral disease. Intralesional therapy is very well-tolerated and addresses the fact that, in patients with advanced regional and injectable stage IV lesions, uncontrolled disease can be very morbid, painful, and disfiguring. “You can deliver a high concentration of drug very easily, providing a very good palliation of symptoms—and durable control may be curative,” he said.
It is likely, as well, that intralesional therapies can provide a priming mechanism for a host-immune response. In essence, the three intralesional therapies cited by Dr. Ross (talimogene laherparepvec [T-VEC], PV-10, and coxsackievirus A21), each through differing mechanisms, selectively invade and lyse tumor cells, leading to the release of tumor-derived antigens and potentiating a systemic T-cell–mediated antitumor response.
Dr. Ross cited clinical trial evidence from T-VEC and PV-10. In the OPTiM phase 3 trial of T-VEC, objective overall responses were reported in 26.4% of patients. Among responders, the complete response (CR) rate was 41%. Fifty percent or higher lesion decreases were reported in 17% of uninjected visceral lesions. The risk of developing visceral or bone metastasis was reduced by 59% compared to the granulocyte-macrophage colony-stimulating factor control.
In the 80-patient phase 2 study of PV-10, a chemoablative agent, the CR rate was 24% in injected lesions and 24% in un injected “bystander” lesions, with a disease control rate (DCR) of 71%. Responses in bystander lesions correlated highly with responses in injected target lesions.
A group showing the strongest responses to several intralesional therapies is patients with stage IIIB/C melanoma. For them, response rates have compared favorably (T-VEC, 52%; PV-10, 49%) to those of the approved systemic immunotherapies (ipilimumab, less than 30%; pembrolizumab, 27–39%; nivolumab, 34–40%). Grade 3–4 adverse event rates, however, are far lower with the intralesional therapies (T-VEC less than 2% versus ipilimumab’s 19%).
The roles for intralesional monotherapy in advanced melanoma are as treatment of unresectable lesions and, potentially, as neoadjuvant therapy before surgery to activate the immune system.
Dr. Andtbacka underscored the superiority of intralesional therapies combined with systemic therapies (i.e., checkpoint inhibitors such as ipilimumab, nivolumab, and pembrolizumab). He listed three factors: 1) intralesional therapies do not add toxicity; 2) they may enhance the effect of checkpoint inhibitors; and 3) response rates with the combinations are better than with either treatment alone.
The best change from baseline in target lesion volume in the CheckMate 067 trial of nivolumab plus ipilimumab was −51.9% for the combination, −34.5% with nivolumab alone, and +5.9% with ipilimumab alone. The 40% grade 3–4 adverse event rate with the combination, however, is a concern, according to Dr. Andtbacka. “There clearly are patients who are not candidates for this combination,” he said.
In the phase 1B trial of ipilimumab plus T-VEC among 18 patients, the DCR was 72%, with durable responses in 44% and complete regression of uninjected nonvisceral and visceral lesions in 39% (52% had 50% or more regression).
Dr. Andtbacka concluded that “the future of oncolytic immunotherapy is in combination with other therapies,” based on his comparison of response rates in advanced unresectable stage III/IV melanoma between monotherapies (ipilimumab, 6–15%; pembrolizumab, 27–38%; nivolumab, 34–40%; T-VEC, 26%) and combination therapies (nivolumab plus ipilimumab, 52%; T-VEC plus ipilimumab, 50%; T-VEC plus pembrolizumab, 56%).
Conference Chairman and Moderator Sanjiv Agarwala, MD, wrapped up the debate stating, “Intralesional therapy is here to stay.” In the course of taking polar positions on intralesional monotherapy, the debaters effectively affirmed their own and Dr. Agarwala’s position.