Lanreotide-octreotide switch in advanced gastrointestinal neuroendocrine tumors (giNETs).

623 Background: Somatostatin analogs (SSA) are the mainstay treatment for advanced giNETs. However, more needs to be understood about the interchangeability and efficacy of commercially available options in sequential use. This study aimed to assess the efficacy of the lanreotide (Lan)—octreotide (Octre) switch in patients with advanced giNETs who experienced no disease progression during octreotide therapy. Methods: This retrospective cohort study analyzed patients with advanced giNETs treated at a single Brazilian cancer center between 2009 and 2021. We included all patients who received octreotide without disease progression and subsequently switched to lanreotide, due to institutional changes in local guidelines. Endpoints included objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS) and overall survival (OS). Results: Among 199 patients with advanced giNETs treated with SSA, 53 transitioned to lanreotide after octreotide and were evaluated. The median age was 54 years (range 21 - 83). The majority had midgut (N=32, 60.4%) or pancreatic (N=16, 30.2%) tumors, with Ki67 index ≤ 2% (N=28, 52.8%) or 3 - 20% (N=20, 37.7%). Carcinoid syndrome was present in 25 patients (47%). Thirty-three patients (62.3%) received octreotide 20 mg before transitioning, while 20 (37.7%) received octreotide 40 mg. The median duration of previous octreotide use before transitioning to lanreotide was 34 months. The ORR and DCR with lanreotide were 10.6% and 89.4%, respectively. With a median follow-up of 34 months, 17 patients experienced progression or death, and the median PFS was not reached. The three-year PFS was 67.2% (95% CI 52.6% - 78.2%). PFS was not affected by previous octreotide dosage (40 mg vs 20 mg: HR 0.63, 95% CI 0.22 - 1.81, P=0.400) or duration (> 36 vs ≤ 36 months: HR 1.44, 95% CI 0.53 - 3.88, P=0.464). With 14 deaths during the follow-up period, the three-year OS was 72.4% (95% CI 57.7% - 82.7%). Conclusions: Our data suggest that switching to lanreotide after octreotide in giNETs without progression maintains the efficacy of SSA, regardless of previous octreotide dosage or duration.