This was a single-center, open-label, single-arm phase II study (ClinicalTrials.gov Identifier: NCT02658812). The study was approved by the institutional review board at The University of Texas MD Anderson Cancer Center. All enrolled patients provided written informed consent.
Eligibility
To be eligible, patients had to have histologic confirmation of breast cancer recurrence with chest wall/cutaneous, subcutaneous, or nodal tumors with or without distant metastases. Patients also had to have at least 1 injectable lesion ≥ 5 mm in longest diameter or multiple injectable lesions with longest diameters totaling ≥ 5 mm. Furthermore, patients had to have received at least 1 systemic therapy regimen for the recurrent disease. An ECOG performance status of 0–1 and adequate organ function were required. Exclusion criteria included disease amenable to surgery with curative intent; metastatic sites that required urgent systemic chemotherapy; known active central nervous system metastases; > 3 lesions per organ in the case of visceral metastases other than lung or lymph node metastases; a history of prior complications from HSV-1 infection; and active autoimmune disease requiring systemic treatment.
Treatment plan
Before administration of T-VEC, all patients underwent imaging and had baseline medical photographs taken to serve as references.
T-VEC was injected into the visible sites of locally recurrent breast cancer or skin metastases on day 1 (cycle 1), day 22 (cycle 2), and every 2 weeks thereafter (cycles ≥ 3) until disease progression. The T-VEC concentration in the initial cycle was 106 PFU/mL, irrespective of HSV-1 serology status. The T-VEC concentration in the second and subsequent cycles was 108 PFU/mL. The total dose of T-VEC injected varied according to tumor size but did not exceed 4.0 mL in any injection cycle [18]. Medical photographs of local lesions were taken before each cycle to record the extent of the disease. Imaging was planned for every 5 cycles until disease progression.
T-VEC was to be permanently discontinued if patients required another anticancer therapeutic agent for any reason, if therapy was delayed > 6 weeks because of a grade 2 or higher immune-mediated adverse event (AE)/allergic reaction, or if therapy was delayed > 4 weeks because of any other T-VEC-related grade 3 or higher toxicities. We designed the study to administer T-VEC for at least 10 cycles (approximately 5 months) unless uncontrolled disease progression was observed. We chose this duration of treatment because a previous study of intralesional T-VEC injections for advanced melanoma showed that more than half of the patients experienced pseudo-progression (an increase in the size of lesions or appearance of new lesions) before they achieved a response, with median time to response of 4.1 months [19]. Uncontrolled disease progression was defined as the rapid growth of multiple measurable or nonmeasurable new lesions or increase in the sum of the longest diameters of existing targeted lesions > 40% from the baseline.
Toxicity assessment
AEs and laboratory results were graded using the Common Terminology Criteria for Adverse Events, version 4.0. Grade 2 or higher nonhematologic AEs and grade 3 or higher hematologic AEs were recorded upon observation by the investigator or report by the patient regardless of whether the AEs were attributed to the investigational product. Grade 2 or higher abnormal laboratory values were recorded as AEs as well. Dose-limiting toxicities were defined as the following AEs when they were at least possibly related to T-VEC: herpetic event requiring treatment, grade 3 or higher immune-mediated AE, grade 2 or higher allergic reaction, grade 3 nonhematologic toxicity lasting more than 3 days, grade 3 or higher nonhematologic abnormal laboratory value failing to respond to medical intervention or leading to hospitalization, grade 2 or higher febrile neutropenia, grade 4 thrombocytopenia, and grade 4 nonhematologic toxicity. In the case of dose-limiting toxicity, T-VEC administration was deferred until the toxicity had resolved to at least grade 1 or returned to baseline levels.
Outcomes
The primary endpoint was the overall response rate, defined as the rate of patients who achieved a partial response or complete response as the best response for the measurable and nonmeasurable disease. The response was evaluated using RECIST version1.1. Secondary endpoints were rates of local overall response/disease control rate, progression-free survival, and overall survival.
Statistical analysis
Progression-free survival and overall survival from the date of treatment initiation were estimated using the Kaplan-Meier method with 95% confidence intervals (CIs). Progression-free survival was defined as the time from treatment initiation until disease progression, and overall survival was defined as the time from treatment initiation until death.