Despite the recent progress, non-metastatic pediatric osteosarcomas have now a 5-year overall survival (OS) around 75% and the metastatic forms are decreasing to 20–30%. To increase these survival rates, new molecular approaches are on development to understand and highlight new candidates for targeted therapies. Tyrosine kinase receptors (TKR) are one of this target class, where new drugs were especially developped, screening now a large spectrum of TKR. After the demonstration among cancers of TKR’s clinical utility as surrogate markers to guide the selection of patients susceptible to respond to these treatments, this success was recently tempered in part because of cancers developping resistance mechanisms to these drugs. A study was conducted to evaluate the interest of these molecular targets among pediatric osteosarcomas.

Materiel and methods: 91 pediatric patients treated homogeneously with the French OS94 protocol were included in this analysis. Allelotyping, real-time quantitative PCR (QPCR), sequencing and immunhistochemistry were performed to analyse the following targets: EGFR, MET, PDGFRA, KIT and ERBB2.

Results and discussion: Most of these targets were rearranged in more than 45% of the population and mainly deleted. Only 11.4% were amplified at MET and 8.6% at PDGFRA. By QPCR, ERBB2 was normal in 78 out of 81 informative patients. Surprinsingly, wild-type KIT protein was amplified in 37%. EGFR was rearranged by allelotyping in 48% and QPCR evaluation just started. MET amplified subgroup is linked to a worst OS than normal and deleted subgroups (p=0.04) whereas PDGFRA amplified tumors tend to be significantly linked to a better patient OS (p=0.08). Considering all amplified subgroups, no ovelap was found as if an osteosarcoma could only be amplified for one gene. This observation could be considered as a way to increase the potential targeted populations where the use of large spectrum TKR inhibitors would be useful in osteosarcoma treatment.

Dysregulation of differentiation genes involved in developmental signaling pathways seems to be a decisive event taking part in the multistep oncogenesis. As high grade osteosarcomas are histologically defined by the presence of malignant osteoblasts producing an osteoid component, we focused in a pediatric cohort, homogeneously treated with the French OS94 protocol, on the genomic status at diagnosis on tumor biopsies of several genes involved in flat and long bone formation.

Material and methods: In 91 pediatric osteosarcomas, allelotyping analysis of FGFRs, TWIST, DERMO1, APC, MET, HGF, and SDC2 was done. After DNA extraction of paired blood and tumor samples, each locus was analysed by microsatellites bordering closely on each side the targeted genes. Complementary real-time quantitative PCR of TWIST, FGFRs and MET genes and sequencing of APC and TWIST were performed to determine gene status.

Results: The allelotyping results support the frequent role of each gene: 53.1% of allelic imbalances (AI) were found in 7p21.2 (TWIST), 35.3% in 2q37.3 (DERMO1), 38% in 5q21 (APC), 42.5% in 7q31 (MET), 45.5% in 7q21.1 (HGF) and 49% for 8q22 (SDC2). TWIST and MET were mainly deleted and no additional APC and TWIST mutations were identified. Surprisingly, FGFR1 to 4 are only abnormal in small subgroups. Significant associations were found combining the presence of MET AI to HGF abnormalities and the presence of MET, TWIST and APC losses. A worse outcome was significantly linked to the presence of MET, TWIST and APC losses (p=0.05, 0.04 and 0.02, respectively) but the subgroup combining MET and HGF abnormalities seems to have a better survival. No correlations was done with other clinical data.

Conclusion: Several genes involved in normal bone development seem to have a role in osteosarcoma development but also to modulate the prognostic outcome of these pediatric patients.