Introduction: Pembrolizumab is a humanized IgG1-κ monoclonal antibody (mAb) targeting the PD-1 receptor that is currently evaluated in clinical trials for the treatment of multiple myeloma (MM). Similar to other mAbs (e.g. daratumumab), it is important to know if pembrolizumab is identified by immunofixation (IFE) and whether it interferes with the detection of endogenous M-protein of patients with MM. Methods: Waste serum of patients with solid malignancies treated with pembrolizumab per routine clinical practice or on clinical trials was collected prior to their next scheduled treatment cycle (trough). All patients had received at least 4 cycles of therapy to allow the drug to reach steady-state. Samples were tested for the presence of a monoclonal protein using both IFE (Sebia Inc.) and nanobody enrichment coupled to MALDI-TOF mass spectrometry (MASS-FIX), as previously described (Mils JR, et al, Clinical Chemistry, 2016). IFE gels and MASS-FIX mass spectra were independently interpreted by the authors (TVK, MAW, AD, DLM). Two samples containing pembrolizumab at 0.05 g/dL and 0.025 g/dL, respectively and one normal serum were used as controls. Results: Of 32 patients, 20 were male. Median age was 62 years. The most common indications for treatment were metastatic melanoma (n=17) and colorectal cancer (n=6). Median dose of the drug was 200mg and all patients received one dose every three weeks. No patients had a detectable IgG kappa band or peak by IFE or MASS-FIX. One patient had a small IgG lambda band on IFE that was not detected by MASS-FIX and one patient had a small IgM lambda peak on MASS-FIX that was not detected by IFE. Pembrolizumab controls were barely detectable by IFE at 0.05 or 0.025 g/dL but were detectable by MASS-FIX. Conclusions: Pembrolizumab, at standard doses, should not interfere with monoclonal protein detection by IFE or MASS-FIX. MASS-FIX can identify monoclonal peaks from Pembrolizumab at low serum concentrations better than IFE.

Disclosures

Dispenzieri: Celgene, Millenium, Pfizer, Janssen: Research Funding.

Author notes

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Asterisk with author names denotes non-ASH members.