R. S. Benjamin

Small-cell osteosarcoma.

Small-cell osteosarcoma, a subtype of osteogenic sarcoma, consists of sheets of round cells that produce an osteoid matrix. It may be confused with Ewing sarcoma if the osteoid matrix is not included in the biopsy. The distinctive radiographic features of an osteoblastic tumor and a pattern of permeative destruction will confirm the histologic diagnosis or indicate the true nature if tumor osteoid is not included in the histological sections. We add 13 patients to the 32 previously reported in the literature. Fourteen (31%) of the 45 are living and well, though three have been followed for only 2 months (Tables 1 and 2). The treatments have been so varied that a statistically significant evaluation cannot be developed. The radiographic features are not distinctive, but the diagnosis may be suggested when a tumor has osteoblastic features in the metaphysis and extends well down into the shaft with a pattern of permeative destruction. The radiographic features are especially important when limited biopsies reveal only sheets of round cells, thus suggesting Ewing sarcoma. The presence of an osteoid-producing tumor as evidenced by osteoblastic new bone formation will lead to the correct diagnosis.

Phase I trial using toxicity severity weights for dose finding of gemcitabine combined with radiation therapy and subsequent surgery for patients with extremity and trunk soft tissue sarcomas

9008 Background: To determine the maximum tolerated dose (MTD) of gemcitabine when provided concurrently with external beam radiation (EBRT) for patients with extremity and superficial trunk soft tissue sarcomas (STS).nnnMETHODSnPreoperative EBRT (50 Gy, 25 daily fractions Mon-Fri) was given for 5 weeks. Gemcitabine was administered at 10 mg/m2/min on days 1, 8, 22, 29, 43, and 50 at a starting dose of 400 mg/m2 and escalated or de-escalated between cohorts in increments of 100 mg/m2 using a new method based on severity weights for each grade of each of 5 different toxicities (myelosuppression, dermatitis, nausea/vomiting, liver, and fatigue). This toxicity severity weight method (TSWM) is a Bayesian procedure that repeatedly assesses the data to find the dose having mean posterior total toxicity burden (TTB) closest to a clinician-defined target of 3.04.nnnRESULTSnEighteen (of 36 planned) patients with radiologically measureable intermediate or high-grade STS have been treated; 16 had completed all therapy at analysis. Histologies included MFH (7), unclassified STS (5), synovial STS (3), and liposarcoma (3). The gemcitabine dose has been progressively escalated to 700 mg/m2 at which the current estimated posterior probability of the TTB is 3.19 (analysis of 15 patients). Five patients have completed treatment at 700 mg/m2 with observed grade 3 or 4 toxicities that included: myelosuppresion without fever (n=2), dermatitis in the radiation field (n=1), hepatotoxicity (n=2), and fatigue (n=2). All 16 patients have undergone surgical resection with microscopically negative surgical margins. Pathological complete responses were observed in 4 tumors, 3 additional tumors had ≥95% tumor necrosis.nnnCONCLUSIONSnGemcitabine-based concurrent chemoradiation appears feasible for extremity and trunk STS. The currently targeted MTD is 700 mg/m2, accrual continues. The TSWM permitted efficient and safe dose escalation using weighted assessment of 5 different, clinically relevant toxicities. Observed histologic responses associated with this regimen are encouraging. [Table: see text].

Outcomes of gastrointestinal stromal tumors (GIST) and other intra-abdominal sarcomas (IAS) in the era of imatinib therapy

9047 Background: IASs are undergoing a diagnostic evolution. In the era of kit immunohistochemistry and imatinib mesylate therapy the outcome of IASs is unknown.nnnMETHODSnWe analyzed 268 consecutive patients who were referred to our institution for evaluation of the diagnosis of GIST from 12/15/00 to 9/1/01. Patients diagnosed with GIST were treated with imatinib mesylate, and patients diagnosed with other IAS were treated with standard sarcoma chemotherapy. A single sarcoma pathologist reviewed all patients tumor blocks. Descriptive statistics were performed from the data obtained and comparisons were made using log rank testing.nnnRESULTSnOf 268 patients, 4 patients were excluded because of diagnoses other than sarcoma. Another 46 patients were excluded because no data were available at the time of this abstract. Of the remaining 218 patients, 159 (72.9%) were GIST and 59 (27.1%) were IAS specifically: 31 leiomyosarcoma, 10 spindle cell tumors, 4 unclassified sarcomas, and 14 other types of sarcoma. The median age of patients diagnosed with GIST was 54 (25 -90) and was 52 (20 -87) for patients diagnosed with other IAS. The most common primary tumor sites for patients with GIST were stomach (37.1%), small bowel (34%), and colon (6.3%); whereas, patients with other intra-abdominal sarcomas occurred in the retroperitoneum (25.4%), abdominal viscera (18.6%), and pelvis (11.9%). The most common metastatic sites seen in patients with GIST were liver (68.6%) and peritoneum (51.6%); whereas other IASs metastasized to the liver (39%) and peritoneum (30.5%). While median survival from the time of diagnosis has not been reached in patients with GIST, in other IAS median survival is 63.8 months. Time to progression in patients with GIST was 16.4 months after imatinib and 5.1 months in patients with IAS treated with standard sarcoma chemotherapy. The 5 year survival rate for GIST is 0.80 (95%CI 0.74,0.86), while for other IAS it is 0.53 (95% CI 0.41,0.67).nnnCONCLUSIONSnSurvival and time to progression are worse for IAS compared to GISTs. New therapies for these tumors are needed. No significant financial relationships to disclose.

Genomic profiling of dedifferentiated liposarcoma compared to matched well-differentiated liposarcoma reveals higher genomic complexity and a common origin

Well-differentiated (WD) liposarcoma is a low-grade mesenchymal tumor with features of mature adipocytes and high propensity for local recurrence. Often, WD patients present with or later progress to a higher-grade nonlipogenic form known as dedifferentiated (DD) liposarcoma. These DD tumors behave more aggressively and can metastasize. Both WD and DD liposarcomas harbor neochromosomes formed from amplifications and rearrangements of Chr 12q that encode oncogenes (MDM2, CDK4, and YEATS2) and adipocytic differentiation factors (HMGA2 and CPM). However, genomic changes associated with progression from WD to DD have not been well-defined. Therefore, we selected patients with matched WD and DD tumors for extensive genomic profiling in order to understand their clonal relationships and to delineate any defining alterations for each entity. Exome and transcriptomic sequencing was performed for 17 patients with both WD and DD diagnoses. Somatic point and copy-number alterations were integrated with transcriptional analyses to determine subtype-associated genomic features and pathways. The results were, on average, that only 8.3% of somatic mutations in WD liposarcoma were shared with their cognate DD component. DD tumors had higher numbers of somatic copy-number losses, amplifications involving Chr 12q, and fusion transcripts than WD tumors. HMGA2 and CPM rearrangements occur more frequently in DD components. The shared somatic mutations indicate a clonal origin for matched WD and DD tumors and show early divergence with ongoing genomic instability due to continual generation and selection of neochromosomes. Stochastic generation and subsequent expression of fusion transcripts from the neochromosome that involve adipogenesis genes such as HMGA2 and CPM may influence the differentiation state of the subsequent tumor.

A phase II study of low-dose protracted irinotecan in patients with advanced sarcomas.

10064 Background: Irinotecan was designed in 1983 and showed activity in preclinical and Phase I trials in solid tumors including osteosarcoma and rhabdomyosarcoma. A wide variety of schedules were used, ranging from weekly to monthly administrations. Dose limiting toxicities were mainly diarrhea and myelosuppression. This IRB-approved phase II trial evaluated the efficacy and toxicity of irinotecan via a low-dose protracted schedule in adult patients with pretreated advanced sarcoma.nnnMETHODSnPatients with inoperable locally advanced or metastatic sarcoma that had received or refused standard chemotherapy for their disease were treated by 16 mg/m2 of irinotecan daily, intravenously over one hour, for 5 days x 2 weeks, with a 2-day rest, repeated in 21-day cycles. The primary end point was tumor response, defined as complete or partial response at 6 weeks or stable disease lasting at least 12 weeks.nnnRESULTSnBetween April 2003 and June 2007, 38 patients (25 males and 13 females) with a median age of 48 years (range, 21-71 years) entered the study. Patients received a median of 2 cycles (range, 0 to 8 cycles). 2 patients underwent surgery and 1 patient is still with no evidence of recurrent disease. 7 patients required early discontinuation of therapy due to toxicities, mainly diarrhea. 16 patients developed progressive disease after 2 cycles, 11 presented stable disease and 6 had partial response after 2 cycles. Among the patients with stable disease after 2 cycles, 3 achieved a partial response, 4 remained stable and 4 progressed after 4 cycles. The response rate was 26%. The median time to progression and overall survival for all 38 patients was 6 weeks and 41 months, respectively. 1 of the 2 chondrosarcoma patients responded to treatment while the other one had transient stable disease. 5 of 7 Ewing sarcoma patients responded to this therapy (71%).nnnCONCLUSIONSnIrinotecan is an interesting therapy option in selected type of sarcoma in advanced and pretreated patient population. Its toxicity profile remains limiting due to diarrhea despite a low dose protracted-schedule delivery. However, myelotoxicity seems reduced on this regimen.

Mechanism of early radiographic response to imatinib in GIST.

10049 Background: Most gastrointestinal stromal tumors (GISTs) harbor activating mutations of the receptor tyrosine kinase KIT, which is inhibited by imatinib (Novartis, Switzerland). Treatment response of GISTs to imatinib is characterized by decreased contrast uptake or tumor size on computed tomographic (CT) imaging. We sought to elucidate the mechanism by which imatinib decreases contrast enhancement of GISTs during the first 3-7 days of therapy.nnnMETHODSnAs part of an IRB-approved, phase II, prospective, randomized clinical trial of preoperative imatinib for GIST patients, radiographic data from 13 patients pre-/post-imatinib treatment were assessed for tumor blood flow (TBF), perfusion and transit time by perfusion CT and tumor response by positron-emission tomography (PET). Tissue specimens pre-/post-imatinib treatment were analyzed for blood vessel density (TBVD)/caliber, stem cell factor (SCF, KIT ligand) expression, KIT phosphorylation and tumor endothelial cell (TEC) apoptosis. GIST and endothelial cell lines (MVEC/HuVEC) were used to assess whether imatinib influences endothelial cell survival through the SCF/KIT signaling pathway.nnnRESULTSn7 of 13 patients with PET response to imatinib demonstrated a mean 45% decrease (p=0.02) in TBF, whereas 6/13 non-responders had a mean 19% increase of TBF (p=0.21) by perfusion CT. TBVD/caliber wasnt affected by imatinib in either group as assessed by immunofluourescence. Imatinib treatment resulted in a 14% increase in TEC apoptosis (p=0.015), compared to only 3% in the non-responders (p=0.52) by immunofluourescent TUNEL assay. Additionally, imatinib significantly blocked KIT phosphorylation of the TECs in imatinib responders but not in non-responders by immunoflourescence. In vitro, imatinib suppressed SCF expression from GIST cells, inhibited SCF-induced KIT phosphorylation by western blot and promoted apoptosis as manifested by increased caspase 3 activation in MVEC.nnnCONCLUSIONSnThe radiographic response of GISTs to imatinib correlates with decreased TBF, TEC apoptosis and SCF/KIT signaling inhibition of MVEC. These findings provide the first mechanistic support of our recently proposed criteria for evaluation of GIST response to imatinib (Choi et al, JCO 2007, 25:1760).

Differential sensitivity of rhabomyosarcoma cell line clones to EGF receptor inhibition with gefitinib

9003 Background: Some rhabdomyosarcomas (RMSs) express the epidermal growth factor receptor (EGFR). Other tumors that overexpress EGFR have a poorer clinical outcome. Gefitinib (Iressa), a competitive inhibitor of EGFR, has demonstrated activity in preclinical and clinical studies.nnnMETHODSnWe designed a cytotoxicity study (MTT) of gefitinib in three RMS cell lines with different levels of expression of EGFR: the RD parent cell line, the RD subclone RD18, and the cell line A673. Apoptosis and cell cycle progression were tested using the APO-BrdU/TUNEL assay, and signal transduction was tested via Western blotting after exposure to gefitinib.nnnRESULTSnElevated EGFR expression was observed in RD18 cells, but EGFR was undetectable in the parent RD cells; expression was low in A673 cells. Exposure of RD18 cells to gefitinib (0.01-10.00 μM) resulted in a dose-dependent decrease in cell viability by 60.8% (p < 0.01), whereas RD cells were resistant. Cell cycle progression was not impacted in any of the RMS cells. RD18 and A673 cells treated with 10 μM gefitinib demonstrated a 3.14- and 8.00-fold increase in apoptosis respectively, whereas RD cells demonstrated no increase. Inhibition of phospho-EGFR and phospho-ERK in RD18 cells was nearly complete at 1 μM and 10 μM gefitinib. A lesser effect was observed in the parent RD cells. Phospho-Akt was inhibited in RD18 cells and minimally in RD cells. In contrast with phospho-ERK, phospho-Akt was minimally inhibited in A673 cells.nnnCONCLUSIONSnWe have demonstrated a model of clonal heterogeneity in EGFR targeted therapy in the gefitinib-resistant RD cell line deficient in EGFR and gefitinib-sensitive RD18 cell line overexpressing EGFR. This was demonstrated by differential signal transduction inhibition and apoptosis in response to gefitinib. Cell cycle inhibition does not appear to be an important component. ERK was consistently affected in all of the cell lines by gefitinib, whereas Akt was not impacted equally. Further studies are warranted to explore the importance of clonal heterogeneity in RMS as well as devise new therapeutic strategies to overcome potentially heterogeneous effects of targeted therapy. No significant financial relationships to disclose.