“Pembrolizumab has antitumor activity in a subset of GEP-NETs patients,” wrote the investigators. “We hypothesized that the lanreotide, by its antitumor effects and reduction of serotonin, a modulator of immunity, would synergize with pembrolizumab in low/intermediate grade GEP-NETs,” wrote the author led by Michael Morse, MD, of Duke Cancer Center.

In the PLANET study (NCT03043664), 22 patients with GEP-NETs who received a median of 2 prior systemic therapies (range 1-9) were treated with 90 mg of lanreotide and 200 mg of pembrolizumab every 3 weeks until disease progression or intolerable toxicity. A median of 6 doses of pembrolizumab (range, 2-15) and 7 doses of lanreotide (range, 2-15) were administered.

Median age at the time of enrollment was 60.9 years (range, 51.1-82.0). Twelve of the patients were male, and 10 were female. To be eligible for the study, participants were required to have a diagnosis of non-resectable, recurrent, or metastatic well- or moderately-differentiated GEP-NETs with disease progression in the last 12 months, received prior somatostatin analogue therapy, a minimum of 1 measurable lesion based on RECIST 1.1 criteria, an ECOG performance status of 0 or 1, adequate organ function, and a tumor mitotic rate of ≤20/10 hpf and/or Ki67 index ≤20%.
Fourteen patients (63.6%) had tumors located within the gastrointestinal tract, of whom 8 patients (36.4%) had their primary tumor site located in the pancreas. The median time since diagnosis for all patients was 5.3 years, with 6 patients having received prior locoregional therapy and 3 patients receiving prior external beam therapy. Of the 12 tumors that were analyzed, 4 had detectable PD-L1 expression and 11 had tumor infiltrating lymphocytes.

PD-L1 expression on a tumour’s cell is one of the mechanisms of immune evasion, since this inhibits functional activity of cytotoxic lymphocytes which will then not attack tumour cells. Tumor-infiltrating lymphocytes are white blood cells that have left the bloodstream and migrated towards a tumour.

The primary end point of the study was overall response rate (ORR), measured according to RECIST 1.1 criteria. Thirty-nine percent of patients showed stable disease (SD) and 52% of patients had progressive disease (PD). ORR, as measured by irRECIST to better assess the effect of immunotherapeutic agents, was 43% SD, 48% PD, with 9% of patients not evaluable.

Secondary end points were progression-free survival (PFS) and overall survival (OS). The median PFS was 5.4 months (95% CI, 1.7-8.3) and median OS at a median follow-up of 15 months was not reached.

Regarding safety, 6 of the 22 patients (27.3%) experienced treatment-related serious adverse events (AEs) including abdominal pain, pneumonitis, colitis, and hyperglycemia, which were all related to treatment with pembrolizumab. The most common treatment-related AE was hypothyroidism (23%), with other notable treatment-related AEs including colitis (9%), hyperglycemia (14%), and pneumonitis (5%). Three patients (13.6%) discontinued treatment due to AEs. No new safety signals were identified in the study. Investigators noted that peripheral blood immune analyses were pending and would be reported subsequently.

“Further studies to identify other approaches to increase the immunogenicity of well/moderately differentiated GEP-NETs are required,” concluded the investigators.

Reference:

Morse M, Halperin DM, Uronis HE, et al. Phase Ib/II study of pembrolizumab with lanreotide depot for advanced, progressive gastroenteropancreatic neuroendocrine tumors (PLANET). Presented at: 2021 American Society of Clinical Oncology (ASCO) Gastrointestinal Cancers Symposium. January 15–17, 2021; virtual. Abstract 369.

Please note that the results have been appended to the Clinical Trial doc referenced above.  The trial is showing as active but not recruiting and that’s most likely because they are assessing whether they can proceed to the next phase.  I will keep this blog live to bring you details when they are published.