P52 RISK STRATIFICATION COMBINING SKY92 GENE EXPRESSION PROFILING AND TRADITIONAL FISH IN MULTIPLE MYELOMA: THE FIRST PROSPECTIVE EVIDENCE IN THE R2-ISS ERA

Abstract

High-risk (HR) multiple myeloma (MM) patients still have a very poor prognosis. However, the definition of HR MM remains controversial. Currently, FISH is the most commonly used method for risk stratification in MM. According to the Second Revised International Staging System (R2-ISS), HR cytogenetics is defined as presence of at least one of the following: del(17p), t(4;14), and 1q CNA. In recent years, gene expression profiling (GEP) approaches, e.g. SKY92, have been developed for detection of HR patients. In the R2-ISS era, however, data on MM risk stratification applying SKY92 in combination with traditional FISH is still lacking. Therefore, we performed the first prospective study evaluating the prognostic value of the combined SKY92 and FISH HR detection in newly diagnosed (ND) and relapsed/refractory (RR) MM. We prospectively collected bone marrow (BM) samples and clinical data of 147 MM patients. Cytogenetics were analyzed on purified CD138 positive MM cells by FISH, and HR cytogenetics was defined according to the R2-ISS classification. SKY92 risk status was determined with MMprofiler gene expression assay. Whole genome sequencing (WGS) was performed to compare the both risk stratification systems SKY92 and FISH. We included 147 patients in our study (NDMM: n=51, RRMM: n=96). SKY92 classification was available for 121 (82.3%) patients. HR SKY92 was significantly enriched in RRMM (40/76) compared with NDMM (6/45) (P<0.0001). RRMM patients with HR SKY92 showed significantly shorter progression free survival (PFS) (P<0.0001) and overall survival (OS) (P=0.0004) than standard-risk (SR). In NDMM, HR SKY92 also indicated a significantly inferior PFS (P=0.001) in comparison with SR. Of note, samples of 26 (17.7%) patients, who showed significantly lower bone marrow infiltration than the remaining patients (median: 25% vs 55%, P=0.038), did not meet the SKY92 quality control criteria. We then combined the SKY92 classification with cytogenetic analyses by FISH, which were available in 99 patients (NDMM: n=33; RRMM: n=66). We noticed a discrepancy between both risk stratification systems, with 44 (44.4%) and 58 (58.6%) patients being classified as HR by SKY92 and FISH, respectively. In total, 28 (42.4%) RRMM patients and 6 (18.2%) NDMM patients displayed HR in both SKY92 and FISH (double-HR). Regarding survival outcome in RRMM, double-HR patients showed the worst PFS (P<0.0001) and OS (P=0.0007). In NDMM, double-HR presented a negative prognostic factor for PFS (P=0.01). To compare the FISH and SKY92 classifications, we performed WGS in 16 patients who exhibited either only HR SKY92 (n=7) or only HR FISH (n=9). Interestingly, 1 patient with bi-allelic TP53 inactivation (deletion + mutation) and 6 patients harbouring 1q CNA were determined as SR by SKY92 but as HR by FISH. The median PFS was not reached after a median follow up of 371 days in these 9 patients. Moreover, 4 out of 7 patients with only HR SKY92 but SR FISH displayed 1q CNA, which was detected only by WGS, and del1p32 was found in 1 patients. Interestingly, we found CRBN mutation in 3 out of 7 patients with only HR SKY92 but SR FISH. The remaining 2 patients did not show any known HR genomic alterations, suggesting that HR MM may be associated with other factors, e.g. epigenetic modifications. Here, we provide the first prospective evidence in the R2-ISS era that advanced risk stratification combining SKY92 and FISH may help to identify the highest-risk MM.