Abstract
BACKGROUND: Small bowel adenocarcinoma (SBA) is a rare cancer with limited treatment strategies beyond first-line platinum-based combination therapy and no established second-line standard. Our recent retrospective study showed that Nectin-4 is frequently highly expressed in SBA and is associated with poorer outcomes, providing a biological rationale for evaluating enfortumab vedotin-a Nectin-4-targeted antibody-drug conjugate. We designed ENVELOPE to evaluate enfortumab vedotin in advanced SBA refractory or intolerant to platinum-based chemotherapy. TRIAL DESIGN: ENVELOPE is a multicenter, single-arm, phase II investigator-initiated trial. Representative eligibility criteria include adults with histologically or cytologically confirmed SBA, measurable disease, Eastern Cooperative Oncology Group performance status 0-1, and prior FOLFOX or CapeOX with progression or intolerance. Enfortumab vedotin is administered at 1.25 mg/kg intravenously on days 1, 8, and 15 of each 28-day cycle until progression or unacceptable toxicity. The primary endpoint is objective response rate (ORR) by blinded independent central review. The null and expected ORRs are 5% and 25%, respectively; an exact binomial design (one-sided alpha = 5%; 90% power) requires 25 assessable patients (planned N = 27). A prospective translational program requires pretreatment tumor tissue, prespecifies Nectin-4 immunohistochemistry as the exploratory biomarker, and collects on-study biopsies/serial blood at baseline, on treatment, and at progression for multi-omics profiling.