[2021 update of the GEFPICS' recommendations for HER2 status assessment in invasive breast cancer in France]. / Mise à jour 2021 des recommandations du GEFPICS pour l'évaluation du statut HER2 dans les cancers infiltrants du sein en France.

The last international guidelines on HER2 determination in breast cancer have been updated in 2018 by the American Society of Clinical Oncology and College of American Pathologists, on the basis of a twenty-year practice and results of numerous clinical trials. Moreover, the emerging HER2-low concept for 1+ and 2+ non amplified breast cancers lead to refine French practices for HER2 status assessment. The GEFPICS group, composed of expert pathologists, herein presents the latest French recommendations for HER2 status evaluation in breast cancer, taking into account the ASCO/CAP guidelines and introducing the HER2-low concept. In the era of personalized medicine, HER2 status assessment remains one of the most important biomarkers in breast cancer and its quality guaranties the optimal patients' care. French pathologists' commitment in theranostic biomarker quality is more than ever required to provide the most efficient cares in oncology.

[GEFPICS' guidelines for management of breast cancer tissue samples in the neoadjuvant setting]. / Recommandations du GEFPICS pour la prise en charge des prélèvements dans le cadre du traitement néoadjuvant du cancer du sein.

Neoadjuvant therapy is an increasing treatment option in the management of breast cancer. The tumor response to neoadjuvant therapy, especially the pathological complete response, is a validated endpoint frequently used in clinical trials. However, there is still a lack of standardization for the surgical specimen management in the neoadjuvant setting. This leads to heterogeneity in the specimen handling and might lead to significant bias for the prognostic assessment of patients or in clinical trials. The GEFPICS group, composed of expert breast cancer pathologists, herein presents guidelines for the management of breast and axillary specimen before treatment (management of biopsy, items of the pathological report) and after neoadjuvant therapy (specimen handling, histological assessment of response, items of the pathological report and response grading systems).

Analysis of tumour-infiltrating lymphocytes reveals two new biologically different subgroups of breast ductal carcinoma in situ.

BACKGROUND: Tumour-infiltrating lymphocytes (TILs) have been demonstrated to significantly influence prognosis and response to therapy of invasive breast cancer (IBC). Thus, it has been suggested that TIL density or/and immunophenotype could serve as biomarkers for selection of IBC patients for immunotherapy. However, much less is known about significance of TILs in breast ductal carcinoma in situ (DCIS). METHODS: We retrospectively investigated TIL density and immunophenotype in 96 pure DCIS and 35 microinvasive carcinomas (miCa). TIL density was assessed on H&E-stained breast biopsy sections as the percentage of tumour stromal area occupied by TILs, and classified into 4 grades: 0 (0%-9%), 1 (10-29%), 2 (30-49%) and 3 (50%-100%). TIL immunophenotype was assessed by immunohistochemistry for CD8, CD4, FoxP3, CD38 or CD20. RESULTS: Compared to pure DCIS, miCa contained significantly more cases with TIL density grade 3 (p = 0.028). Concordantly, CD8+, CD4+ and CD38+ cells were more numerous in miCa than in pure DCIS. In the pure DCIS subgroup with TIL density grades 2 and 3, all TIL subpopulations were more numerous than in the pure DCIS with TIL density grades 0 and 1, however the ratio between T-lymphocytes (CD8+ and CD4+) and B-lymphocytes (CD20+) was significantly lower (p = 0.029). On the other side, this ratio was significantly higher in miCa, in comparison with pure DCIS having TIL density grades 2 and 3 (p = 0.017). By cluster analysis of tumour cell pathobiological features we demonstrated similarity between miCa and the pure DCIS with TIL density grades 2 and 3. The only significant difference between those two categories was in the ratio of T- to B-TILs, higher in miCa. CONCLUSION: Results indicate that TIL density level can distinguish 2 biologically different DCIS subgroups, one of which (DCIS with ≥30% TILs, the TIL-rich DCIS) is like miCa. Similarity of TIL-rich pure DCIS and miCa as well as the role of B-lymphocytes in DCIS invasiveness are worth further investigating with regards to the potential development of immunotherapy-based prevention of DCIS progression.

Small rigid platforms functionalization with quaternary ammonium: targeting extracellular matrix of chondrosarcoma.

This work takes place in the "cartilage targeting strategy", consisting in using the quaternary ammonium (QA) function as a vector to proteoglycans (PGs) of extracellular matrix (ECM). The objective was to demonstrate that QA could address gadolinium based small rigid platforms (SRP) to PG-rich tumors. SRP were functionalized with QA, radiolabeled with (111)Indium and evaluated for biodistribution in vivo, respectively to non functionalized SRP, in two experimental models: (i) the HEMCSS human xenograft model; (ii) the Swarm rat chondrosarcoma (SRC) orthotopic model. The contribution of cellular uptake to tumoral accumulation of nano-objects was also determined from in vitro binding. In the SRC model expressing a highly and homogeneously distributed PG content, tumor accumulation and retention of SRP@QA were increased by 40% as compared to non-functionalized SRP. When considering the radiosensitizing potential of gadolinium based SRP, these results provide hopes for the radiobiological approach of highly resistant tumor such as chondrosarcoma. FROM THE CLINICAL EDITOR: In this study, gadolinium-based complexing DOTA-surfaced small polysiloxane nanoparticles were functionalized with quaternary ammonium derivatives that target the extracellular matrix of chondrosarcoma. The authors demonstrate in a rat model that the use of these constructs results in a 40% increase of tumor accumulation and retention compared to non-functionalized (and otherwise same) platforms. Similar approaches would be welcome additions to the clinical armamentarium addressing chondrosarcoma.

[Pre-analytical stage for biomarker assessment in breast cancer: 2014 update of the GEFPICS' guidelines in France]. / Recommandations du GEFPICS concernant la phase pré-analytique pour l'évaluation de HER2 et des récepteurs hormonaux dans le cancer du sein : mise à jour 2014.

Biomarker assessment of breast cancer tumor samples is part of the routine workflow of pathology laboratories. International guidelines have recently been updated, with special regards to the pre-analytical steps that are critical for the quality of immunohistochemical and in situ hybridization procedures, whatever the biomarker analyzed. Fixation and specimen handling protocols must be standardized, validated and carefully tracked. Cooperation and training of the personnel involved in the specimen workflow (e.g. radiologists, surgeons, nurses, technicians and pathologists) are of paramount importance. The GEFPICS' update of the recommendations herein details and comments the different steps of the pre-analytical process. Application of these guidelines and participation to quality insurance programs are mandatory to ensure the correct evaluation of oncotheranostic biomarkers.

[2014 update of the GEFPICS' recommendations for HER2 status determination in breast cancers in France]. / Mise à jour 2014 des recommandations du GEFPICS pour l'évaluation du statut HER2 dans les cancers du sein en France.

International guidelines on HER2 determination in breast cancer have just been updated by the American Society of Clinical Oncology (ASCO) and College of American Pathologists (CAP), on the basis of more than ten-year practice, results of clinical trials and concordance studies. The GEFPICS group, composed of expert pathologists in breast cancer, herein presents these recommendations, adapted to the French routine practice. These guidelines highlight the possible diagnosis difficulties with regards to HER2 status determination, such as intra-tumor heterogeneity, special histological subtypes and biomarker re-evaluation during metastatic relapse. Pre-analytical issues and updated scoring criteria (especially for equivocal cases) are detailed, in order to decrease the occurrence of false negative cases. In the era of personalized medicine, pathologists are more than ever involved in the quality of oncotheranostic biomarker evaluation.

[Diagnostic approach for breast cancer classification]. / Démarche diagnostique dans cancer du sein, classification.

The pathologist is involved at various steps in the management of a patient with breast cancer and in the therapeutic decision. First, the pathologist confirms a diagnosis of malignancy on cytology specimens, microbiopsies and surgical specimens. During the surgery, through the frozen section, the pathologist specifies the surgical limits and collects specimens for research purposes. Then the pathologist evaluates the parameters needed to establish the final diagnosis, the prognosis and the identification of predictive factors, using ancillary techniques such as immunohistochemistry, in situ hybridization or molecular techniques. Mandatory elements to be included in the final pathological report are size, histological type, SBR grade modified by Elston and Ellis, the presence or absence of vascular or lymphatic peritumoral emboli (prognostic parameters), the status of resection margins (local relapse risk) and the status of hormonal receptor and HER2 (predictive parameters).

Quaternary ammonium-melphalan conjugate for anticancer therapy of chondrosarcoma: in vitro and in vivo preclinical studies.

Cartilage tumours present ongoing therapeutic challenges due to their chondrogenic extracellular matrix that potentially hampers drug delivery, their low percentage of dividing cells, and their poor vascularity. In this context, and based on the affinity of the quaternary ammonium moiety for proteoglycans (PG), we developed a strategy that uses the quaternary ammonium function to selectively deliver DNA alkylating agents to the cartilage tumour tissue. We engineered the quaternary ammonium derivative of melphalan (Mel-AQ) and assessed its antitumoural activity in vitro and in vivo. In vitro, micromolar concentrations of Mel-AQ inhibited the proliferation of human HEMC-SS chondrosarcoma and Saos-2 osteosarcoma cell lines. Moreover, 24-h incubation with 20 µM Mel-AQ induced a 2.5-fold increase in S population and a 1.5-fold increase in subG0G1 population compared to controls. In vivo, Mel-AQ demonstrated antitumour activity in the orthotopic model of primary Swarm rat chondrosarcoma. When given to chondrosarcoma-bearing rats (three doses of 16 µmol/kg at days 8, 12 and 16 post-implant), Mel-AQ demonstrated an optimal antitumour effect at day 43, when tumour cell growth inhibition peaked at 69%. Interestingly, the treatment protocol was proved well tolerated, since the animals showed no weight loss over the course of the study. This antitumoural effect was assessed in vivo by scintigraphic imaging using (99m)Tc-NTP 15-5 developed in our lab as a PG-targeting radiotracer, and tumour tissue was analyzed at study-end by biochemical PG assay with Alcian blue staining. Mel-AQ treatment led to a significant decrease in the PG content of tumoural tissue. These experimental results highlighted the promising antitumour potential of Mel-AQ as a PG-targeting strategy for therapeutic management of chondrosarcoma.

Embolization and endothelial ablation with chitosan and sodium sotradecol sulfate: preliminary results in an animal model.

PURPOSE: To investigate whether embolization with chitosan hydrogel (CH) with or without a sclerosant (sodium tetradecyl sulphate, STS) can induce chemical endothelial ablation and prevent endothelial recanalization in a rabbit model. METHODS: Chitosan radiopaque thermogels were prepared using chitosan, ß-glycerophosphate, iopamidol, and different STS concentrations. Each auricular artery of 14 New Zealand White rabbits was cannulated and injected with 0.6 mL of chitosan (CH0; n = 14) on one side and either saline (n = 3), chitosan and 1% STS (CH1; n = 6), or chitosan and 3% STS (CH3; n = 6) in the contralateral side. Immediately after embolization and at 1, 7, 14, and 30 days, auricular artery patency and percentage of recanalization were assessed by visual inspection; microcirculation was evaluated using laser Doppler imaging (LDI). The rabbits were sacrificed at 30 days to assess endothelial ablation and inflammatory response by histological analyses. RESULTS: All arteries were catheterized and embolized with success. All saline-injected arteries rapidly recovered normal flow. The length of embolization was greater with CH3 than CH1 or CH0, regardless of the time observed (p<0.001). No difference in recanalization length was found among the gels (p = 0.07). Destruction of arterial wall was frequently observed independent of embolizing agent. Foreign body reaction was more frequent with CH3 as compared with CH1 and CH0 (p = 0.0070 and 0.0058, respectively). After 30 days, hypervascularization was observed on LDI only with CH0; it was attributed to intra- or perivascular neovessels and inflammatory response on pathological analysis. The vascular modifications appeared to be more homogenous across the length of embolization with CH3 than the other formulations. CONCLUSION: The viscosity obtained with chitosan and 3% STS permits better control during injection and longer vascular occlusion. These findings, combined with the intravascular neovascularization observed with CH0, led us to prefer the combination with STS.

A"Proteoglycan targeting strategy" for the scintigraphic imaging and monitoring of the swarm rat chondrosarcoma orthotopic model.

Our lab developed (99m)Tc-NTP 15-5 radiotracer as targeting proteoglycans (PGs) for the scintigraphic imaging of joint. This paper reports preclinical results of (99m)Tc-NTP 15-5 imaging of an orthotopic model of Swarm rat chondrosarcoma (SRC). (99m)Tc-NTP 15-5 imaging of SRC-bearing and sham-operated animals was performed and quantified at regular intervals after surgery and compared to bone scintigraphy and tumoural volume. Tumours were characterized by histology and PG assay. SRC exhibited a significant (99m)Tc-NTP 15-5 uptake at very early stage after implant (with tumour/muscle ratio of 1.61 ± 0.14), whereas no measurable tumour was evidenced. As tumour grew, mean tumour/muscle ratio was increased by 2.4, between the early and late stage of pathology. Bone scintigraphy failed to image chondrosarcoma, even at the later stage of study. (99m)Tc-NTP 15-5 imaging provided a suitable set of quantitative criteria for the in vivo characterization of chondrosarcoma behaviour in bone environment, useful for achieving a greater understanding of the pathology.

Quantification of Immune Variables from Liquid Biopsy in Breast Cancer Patients Links Vδ2+ γδ T Cell Alterations with Lymph Node Invasion.

The rationale for therapeutic targeting of Vδ2+ γδ T cells in breast cancer is strongly supported by in vitro and murine preclinical investigations, characterizing them as potent breast tumor cell killers and source of Th1-related cytokines, backing cytotoxic αß T cells. Nonetheless, insights regarding Vδ2+ γδ T cell phenotypic alterations in human breast cancers are still lacking. This paucity of information is partly due to the challenging scarcity of these cells in surgical specimens. αß T cell phenotypic alterations occurring in the tumor bed are detectable in the periphery and correlate with adverse clinical outcomes. Thus, we sought to determine through an exploratory study whether Vδ2+ γδ T cells phenotypic changes can be detected within breast cancer patients' peripheral blood, along with association with tumor progression. By using mass cytometry, we quantified 130 immune variables from untreated breast cancer patients' peripheral blood. Supervised analyses and dimensionality reduction algorithms evidenced circulating Vδ2+ γδ T cell phenotypic alterations already established at diagnosis. Foremost, terminally differentiated Vδ2+ γδ T cells displaying phenotypes of exhausted senescent T cells associated with lymph node involvement. Thereby, our results support Vδ2+ γδ T cells implication in breast cancer pathogenesis and progression, besides shedding light on liquid biopsies to monitor surrogate markers of tumor-infiltrating Vδ2+ γδ T cell antitumor activity.

When to do surgical resection for atypical breast lesions: Results of a prospective cohort of 518 lesions.

AIM: There is no consensual indication for surgical resection after diagnosis on per-cutaneous biopsy of borderline breast lesions (B3). We evaluate under-evaluation rate of per-cutaneous biopsy and predictive factors of under-evaluation. We analyze accuracy of reported decision-making tools. METHODS: We conduct a prospective multicentric study including, atypic-ductal hyperplasia (ADH), atypic-lobular hyperplasia (ALH), atypic-cylindro-cubic metaplasia (FEA), papilloma, radial scars (RS) and phyllod tumors. When several B3 lesions were associated, the more severe lesion was used to classify the lesion. We determined breast cancers (BC) rate and histologic type. Among 478 patients, 518 B3 lesions were studied: 15.1% (78) FEA, 48.6% (252) ADH, 16.8% (n = 87) ALH, 5.4% (n = 28) RS, 12% (n = 62) papilloma, 0.8% (n = 4) phyllod tumors and 0,8% (n = 4) with a suspicious low grade DCIS. More than 1 lesion was identified in 31.9% (165) of cases. A surgical resection was performed for 86.3% (447/518) lesions. Significant factors of surgical resection were: residual micro-calcification after biopsy (OR: 2.7) and type of B3 lesion. RESULTS: Overall BC rate was 15.3% (68/445) with 79.4% (54) in-situ carcinomas. According to B3 lesions, BC rates were 12.9% for FEA, 20% for ADH, 11.6% for ALH, 3.7% for RS, 8.8% for papilloma and 25% for suspicious in-situ carcinoma. A score has been calculated and patients were distributed in 3 groups. Patient's rates without BC were respectively: 100%, 80.4% and 80.6% (p = 0.029). CONCLUSION: In conclusion, it could be suggested to avoided complementary surgical resection in case of good radio-pathologic concordance and low probability of BC.

Ovarian epithelial dysplasia and prophylactic oophorectomy for genetic risk.

UNLABELLED: To make an accurate histopathological description of ovarian dysplasia in a population at genetic risk of ovarian cancer and devise an ovarian dysplasia score. MATERIALS AND METHODS: In this retrospective cohort study, 90 patients who had undergone bilateral oophorectomy or ovarian cystectomy between 1992 and 2005 and whose ovaries were reported as normal were divided into two groups: Group A comprising prophylactic oophorectomies for genetic predisposition (N = 28), and Group B or control group, fertile and non-cancerous (N = 62). Eleven epithelial cytological and architectural features were defined. Ovaries were analysed and reviewed by four pathologists blinded to clinical data. An ovarian dysplasia score was devised to quantify extent of ovarian epithelial abnormalities. The degrees of ovarian epithelial abnormalities (dysplasia scores) were compared between the two groups. RESULTS: Mean dysplasia score was significantly higher in Group A (prophylactic oophorectomies) than in Group B (control group) (9.67 vs. 4.19, P < 0.001). In Group A, we observed a gradation in the severity of the dysplastic lesions between (i) proven BRCA mutations and prophylactic oophorectomies without mutations (11.26 vs. 8.1), and (ii) according to age (10.27 after age 50 years vs. 8.6 before age 50 years, P = 0.2962). CONCLUSION: These results suggest abnormalities in ovaries from high risk women. The ovarian dysplasia may be a pre-malignant, non-invasive histological lesion that could be an important step in early neoplasia.

Doxycycline and its quaternary ammonium derivative for adjuvant therapies of chondrosarcoma.

PURPOSE: This study was conducted during the development of innovative treatment targeting the microenvironment of chondrosarcoma. In this context, MMP inhibitors were conjugated with a quaternary ammonium (QA) function as a targeting ligand to proteoglycans of chondrosarcoma extracellular matrix. Here we report the proof of concept of this strategy applied to the MMP13 inhibitor, doxycycline (Dox). METHODS: A quaternary ammonium derivative of the MMP13 inhibitor doxycycline (QA-Dox) was synthesized, and its anticancer activity was evaluated in the Swarm rat chondrosarcoma (SRC) model compared with the parent drug doxycycline, in vitro and in vivo. In vivo, dox and QA-Dox efficiency was assessed at equimolar doses according to a q4dx4 schedule by monitoring tumour volume by MRI and PG-targeted scintigraphy. Molecular mechanism (MMP13 expression, proteoglycan level) and histology studies were performed on tumours. RESULTS: The link of QA targeting function to Dox maintained the MMP13 inhibitory activity in vitro. Interestingly, the bacteriostatic activity was lost. SRC cells incubated with both drugs were blocked in S and G2 M phases. Tumour growth inhibition (confirmed by histology) was observed for both Dox and QA-Dox. Undesirable blood effects (leukocyte decrease) were reduced when Dox was targeted to tumour tissue using the QA function. CONCLUSIONS: In the SRC model, the MMP13 inhibitor Dox and its QA derivative are promising as adjuvant therapies for chondrosarcoma management.

TERT promoter status and gene copy number gains: effect on TERT expression and association with prognosis in breast cancer.

Upregulation of the telomerase reverse transcriptase (TERT) gene in human cancers leads to telomerase activation, which contributes to the growth advantage and survival of tumor cells. Molecular mechanisms of TERT upregulation are complex, tumor-specific and can be clinically relevant. To investigate these mechanisms in breast cancer, we sequenced the TERT promoter, evaluated TERT copy number changes and assessed the expression of the MYC oncogene, a known transcriptional TERT regulator, in two breast cancer cohorts comprising a total of 122 patients. No activating TERT promoter mutations were found, suggesting that this mutational mechanism is not likely to be involved in TERT upregulation in breast cancer. The T349C promoter polymorphism found in up to 50% of cases was not correlated with TERT expression, but T349C carriers had significantly shorter disease-free survival. TERT gains (15-25% of cases) were strongly correlated with increased TERT mRNA expression and worse patient prognosis in terms of disease-free and overall survival. Particularly aggressive breast cancers were characterized by an association of TERT gains with MYC overexpression. These results evidence a significant effect of gene copy number gain on the level of TERT expression and provide a new insight into the clinical significance of TERT and MYC upregulation in breast cancer.

Proteoglycans as Target for an Innovative Therapeutic Approach in Chondrosarcoma: Preclinical Proof of Concept.

To date, surgery remains the only option for the treatment of chondrosarcoma, which is radio- and chemoresistant due in part to its large extracellular matrix (ECM) and poor vascularity. In case of unresectable locally advanced or metastatic diseases with a poor prognosis, improving the management of chondrosarcoma still remains a challenge. Our team developed an attractive approach of improvement of the therapeutic index of chemotherapy by targeting proteoglycan (PG)-rich tissues using a quaternary ammonium (QA) function conjugated to melphalan (Mel). First of all, we demonstrated the crucial role of the QA carrier for binding to aggrecan by surface plasmon resonance. In the orthotopic model of Swarm rat chondrosarcoma, an in vivo biodistribution study of Mel and its QA derivative (Mel-QA), radiolabeled with tritium, showed rapid radioactivity accumulation in healthy cartilaginous tissues and tumor after [3H]-Mel-QA injection. The higher T/M ratio of the QA derivative suggests some advantage of QA-active targeting of chondrosarcoma. The antitumoral effects were characterized by tumor volume assessment, in vivo 99mTc-NTP 15-5 scintigraphic imaging of PGs, 1H-HRMAS NMR spectroscopy, and histology. The conjugation of a QA function to Mel did not hamper its in vivo efficiency and strongly improved the tolerability of Mel leading to a significant decrease of side effects (hematologic analyses and body weight monitoring). Thus, QA conjugation leads to a significant improvement of the therapeutic index, which is essential in oncology and enable repeated cycles of chemotherapy in patients with chondrosarcoma. Mol Cancer Ther; 15(11); 2575-85. ©2016 AACR.

99mTc-NTP 15-5 assessment of the early therapeutic response of chondrosarcoma to zoledronic acid in the Swarm rat orthotopic model.

BACKGROUND: Since proteoglycans (PGs) appear as key partners in chondrosarcoma biology, PG-targeted imaging using the radiotracer 99mTc-N-(triethylammonium)-3-propyl-[15]ane-N5 (99mTc-NTP 15-5) developed by our group was previously demonstrated to be a good single-photon emission computed tomography tracer for cartilage neoplasms. We therefore initiated this new preclinical study to evaluate the relevance of 99mTc-NTP 15-5 imaging for the in vivo monitoring and quantitative assessment of chondrosarcoma response to zoledronic acid (ZOL) in the Swarm rat orthotopic model. FINDINGS: Rats bearing chondrosarcoma in the orthotopic paratibial location were treated by ZOL (100 µg/kg, subcutaneously) or phosphate-buffered saline, twice a week, from day 4 to day 48 post-tumor implantation. 99mTc-NTP 15-5 imaging was performed at regular intervals with the target-to-background ratio (TBR) determined. Tumor volume was monitored using a calliper, and histology was performed at the end of the study. From day 11 to day 48, mean TBR values ranged from 1.7 ± 0.6 to 2.3 ± 0.6 in ZOL-treated rats and from 2.1 ± 1.0 to 4.9 ± 0.9 in controls. Tumor growth inhibition was evidenced using a calliper from day 24 and associated to a decrease in PG content in treated tumor tissues (confirmed by histology). CONCLUSIONS: This work demonstrated two proofs of concept: (1) biphosphonate therapy could be a promising therapeutic approach for chondrosarcoma; (2) 99mTc-NTP 15-5 is expected to offer a novel imaging modality for the in vivo evaluation of the extracellular matrix features of chondrosarcoma, which could be useful for the follow-up and quantitative assessment of proteoglycan 'downregulation' associated to the response to therapeutic attempts.

Relevance of the POS-1 orthotopic model as an "imaging model" for in vivo and simultaneous monitoring of tumor proliferation and bone remodeling in osteosarcoma.

INTRODUCTION: Osteosarcoma (OS) management requires a better understanding of tumor/bone interactions in vivo during disease progression. Using [(18)F]-FDG and [(99m)Tc]-HMDP imaging, we assessed a methodology for an in vivo quantitative characterization of an orthotopic model of osteolytic OS on the basis of (1) tumor proliferation, (2) tumor and bone metabolic activities, and (3) bone remodeling. METHODS: POS-1 tumor bearing mice were monitored in vivo over a 26-day period, with tumor and bone metabolic volumes (TMV and BMV, respectively) being determined from [(18)F]-FDG, bone remodeling from [(99m)Tc]-HMDP, and tumoral volume from micro- computed tomography scans. RESULTS: From day 10, [(18)F]-FDG strongly accumulated within POS-1 tumor, with a tumor/muscle ratio of 3.7 ± 0.8. TMV and BMV increased as pathology progressed: TMV increased at early stage of pathology (from 56%) whereas BMV strongly increased (from 113%) during late stage. From [(99m)Tc]-HMDP imaging, bone remodeling features were evidenced within the distal region of tibia bearing the tumor, with a mean scintigraphic ratio of 1.36 ± 0.11 at day 12, that reached value of 2.53 ± 0.19 at day 26. CONCLUSIONS: Our results validated the POS-1 orthotopic model as "OS imaging model," that could serve for evaluating in vivo therapies targeting tumor proliferation and/or bone remodeling in OS.