Tumor Necrosis in Pediatric Osteosarcoma: Impact of Modern Therapies

Tumor necrosis following preoperative chemotherapy in patients with osteosarcoma is a predictor of overall survival. With modern therapies, 45% of patients are expected to achieve more than 90% tumor necrosis. Investigators at the authors’ center, however, increasingly noted that patients were experiencing inferior necrosis responses. A retrospective study of treated patients at the center was undertaken to examine this. The purpose of this study was to determine (1) whether the number of patients with favorable histological responses had changed over time and (2) whether the percentage of patients with favorable responses was similar to published outcomes. Chart reviews were performed on patients treated from 1993 to 2003 according to the Pediatric Oncology Group 9351, regimen A protocol. Twenty-one patients met all eligibility requirements; 52% of patients had more than 90% necrosis. No correlation existed between degree of necrosis and year of treatment (r = 0.06; P = .8). Patients with osteosarcoma treated at the authors’ institution have comparable tumor necrosis responses to published outcomes, and no change occurred over time. This study stresses the importance of rigorous retrospective reviews before implementing treatment changes.

The landscape of fusion transcripts in spitzoid melanoma and biologically indeterminate spitzoid tumors by RNA sequencing

Kinase activation by chromosomal translocations is a common mechanism that drives tumorigenesis in spitzoid neoplasms. To explore the landscape of fusion transcripts in these tumors, we performed whole-transcriptome sequencing using formalin-fixed, paraffin-embedded (FFPE) tissues in malignant or biologically indeterminate spitzoid tumors from 7 patients (age 2-14 years). RNA sequence libraries enriched for coding regions were prepared and the sequencing was analyzed by a novel assembly-based algorithm designed for detecting complex fusions. In addition, tumor samples were screened for hotspot TERT promoter mutations, and telomerase expression was assessed by TERT mRNA in situ hybridization (ISH). Two patients had widespread metastasis and subsequently died of disease, and 5 patients had a benign clinical course on limited follow-up (mean: 30 months). RNA sequencing and TERT mRNA ISH were successful in six tumors and unsuccessful in one disseminating tumor because of low RNA quality. RNA sequencing identified a kinase fusion in five of the six sequenced tumors: TPM3-NTRK1 (2 tumors), complex rearrangements involving TPM3, ALK, and IL6R (1 tumor), BAIAP2L1-BRAF (1 tumor), and EML4-BRAF (1 disseminating tumor). All predicted chimeric transcripts were expressed at high levels and contained the intact kinase domain. In addition, two tumors each contained a second fusion gene, ARID1B-SNX9 or PTPRZ1-NFAM1. The detected chimeric genes were validated by home-brew break-apart or fusion fluorescence in situ hybridization (FISH). The two disseminating tumors each harbored the TERT promoter -124C>T (Chr 5:1,295,228 hg19 coordinate) mutation, whereas the remaining five tumors retained the wild-type gene. The presence of the -124C>T mutation correlated with telomerase expression by TERT mRNA ISH. In summary, we demonstrated complex fusion transcripts and novel partner genes for BRAF by RNA sequencing of FFPE samples. The diversity of gene fusions demonstrated by RNA sequencing defines the molecular heterogeneity of spitzoid neoplasms.

Abstract A09: Preclinical trial using the combination of panobinostat with bortezomib in human orthotopic xenograft mouse models of rhabdomyosarcoma

Background: Rhabdomyosarcoma (RMS) is an aggressive malignancy of childhood which has a poor prognosis when it has metastasized. Although there has been improvement in overall survival for low and intermediate risk patients, there has been no significant improvement in outcome in the past 25 years for patients with high risk disease. Orthotopic patient derived mouse xenografts (O-PDXs) have been created from patients with high risk disease to facilitate preclinical trials and provide useful information regarding efficacy and toxicity of novel therapeutic agents. Histone deacetylases (HDAC) have emerged as a relevant clinical target in RMS and other pediatric solid tumors, and the synergistic combination of HDAC inhibitors with proteasome inhibitors has led to increased cellular stress and apoptosis in other malignancies. The HDAC inhibitor panobinostat combined with bortezomib, a proteasome inhibitor, is a combination currently in consideration for clinical trial development for this patient population.

Methods: Orthotopic xenografts were created by injecting patient derived RMS cells into the hind-leg muscle of CD-1 nude mice. Detailed molecular and histopathologic characterization of the tumors was performed to ensure they recapitulate human disease. Primary cultures of dissociated O-PDXs were used for high-throughput drug screening in dose response. Pharmacokinetic studies on RMS tumor-bearing mice were performed to determine matched human AUC-guided dosing and schedule of chemotherapy agents. Preclinical phase I tolerability studies were performed for all drug combinations. The following preclinical phase II study was performed using 2 different O-PDXs (SJRBH000026_X1, SJRHB012_Y) both derived from patients with metastatic recurrent embryonal RMS:

(SJRBH000026_X1, SJRHB012_Y)

Group 1 (n = 5, n = 4) Panobinostat/Bortezomib

Group 2 (n = 3, n = 3) Vincristine/Irinotecan (relapse standard of care)

Group 3 (n = 3, n = 3) Control (no chemotherapy)

Enrollment into the 3 treatment groups was randomized for each of the O-PDXs tested. Two courses of therapy were given on a clinically relevant schedule with each course consisting of 21 days. The study endpoint was reached and mice were classified as progressive disease when tumor approached 20% of body weight.

Results: Both O-PDXs tested in vitro were found to be highly sensitive to panobinostat and bortezomib with EC50 values in the nanomolar range for both drugs. Drug combinations were found to be well tolerated in preclinical phase I studies at the doses tested with only temporary mild dehydration observed in the panobinostat/bortezomib group. In the preclinical phase II study, mice in group 1 were found to have an average survival of 16.5 days (avg. of 11 days, 22 days respectively). Mice receiving the standard of care therapy (group 2) survived an average of 40.7 days (avg. of 49 days, 32.3 days respectively). Mice in group 3 were determined to have progressive disease on average at 17 days (avg. of 12.3 days, 21.7 days respectively).

Conclusions: On the basis of preclinical in vitro data, combining HDAC and proteasome inhibitors is an attractive strategy for RMS and was found to be tolerable in preclinical phase I studies. However, the use of this combination in O-PDXs failed to show meaningful efficacy. The lack of response in relevant RMS models raises concerns about the sensitivity observed in in vitro studies and additional biologic and pharmacokinetic studies are indicated to identify factors leading to this discrepancy prior to further clinical development of these agents for this patient population.

Citation Format: Elizabeth Stewart, Cori Bradley, Anang Shelat, Alberto Pappo, Michael A. Dyer. Preclinical trial using the combination of panobinostat with bortezomib in human orthotopic xenograft mouse models of rhabdomyosarcoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr A09.

TERT Promoter Mutations Are Predictive of Aggressive Clinical Behavior in Patients with Spitzoid Melanocytic Neoplasms

Spitzoid neoplasms constitute a morphologically distinct category of melanocytic tumors, encompassing Spitz nevus (benign), atypical Spitz tumor (intermediate malignant potential), and spitzoid melanoma (fully malignant). Currently, no reliable histopathological criteria or molecular marker is known to distinguish borderline from overtly malignant neoplasms. Because TERT promoter (TERT-p) mutations are common in inherently aggressive cutaneous conventional melanoma, we sought to evaluate their prognostic significance in spitzoid neoplasms. We analyzed tumors labeled as atypical Spitz tumor or spitzoid melanoma from 56 patients with available follow-up data for the association of TERT-p mutations, biallelic CDKN2A deletion, biallelic PTEN deletion, kinase fusions, BRAF/NRAS mutations, nodal status, and histopathological parameters with risk of hematogenous metastasis. Four patients died of disseminated disease and 52 patients were alive and disease free without extranodal metastasis (median follow-up, 32.5 months). We found TERT-p mutations in samples from the 4 patients who developed hematogenous metastasis but in none of tumors from patients who had favorable outcomes. Presence of TERT-p mutations was the most significant predictor of haematogenous dissemination (P < 0.0001) among variables analyzed. We conclude that TERT-p mutations identify a clinically high-risk subset of patients with spitzoid tumors. Application of TERT-p mutational assays for risk stratification in the clinic requires large-scale validation.

The Childhood Solid Tumor Network: A new resource for the developmental biology and oncology research communities

Significant advances have been made over the past 25 years in our understanding of the most common adult solid tumors such as breast, colon, lung and prostate cancer. Much less is known about childhood solid tumors because they are rare and because they originate in developing organs during fetal development, childhood and adolescence. It can be very difficult to study the cellular origins of pediatric solid tumors in developing organs characterized by rapid proliferative expansion, growth factor signaling, developmental angiogenesis, programmed cell death, tissue reorganization and cell migration. Not only has the etiology of pediatric cancer remained elusive because of their developmental origins, but it also makes it more difficult to treat. Molecular targeted therapeutics that alter developmental pathway signaling may have devastating effects on normal organ development. Therefore, basic research focused on the mechanisms of development provides an essential foundation for pediatric solid tumor translational research. In this article, we describe new resources available for the developmental biology and oncology research communities. In a companion paper, we present the detailed characterization of an orthotopic xenograft of a pediatric solid tumor derived from sympathoadrenal lineage during development.

Germline ETV6 Mutations Confer Susceptibility to Acute Lymphoblastic Leukemia and Thrombocytopenia

Somatic mutations affecting ETV6 often occur in acute lymphoblastic leukemia (ALL), the most common childhood malignancy. The genetic factors that predispose to ALL remain poorly understood. Here we identify a novel germline ETV6 p. L349P mutation in a kindred affected by thrombocytopenia and ALL. A second ETV6 p. N385fs mutation was identified in an unrelated kindred characterized by thrombocytopenia, ALL and secondary myelodysplasia/acute myeloid leukemia. Leukemic cells from the proband in the second kindred showed deletion of wild type ETV6 with retention of the ETV6 p. N385fs. Enforced expression of the ETV6 mutants revealed normal transcript and protein levels, but impaired nuclear localization. Accordingly, these mutants exhibited significantly reduced ability to regulate the transcription of ETV6 target genes. Our findings highlight a novel role for ETV6 in leukemia predisposition.

The role of chest computed tomography (CT) as a surveillance tool in children with high-risk neuroblastoma

BACKGROUND

Standardization of imaging obtained in children with neuroblastoma is not well established. This study examines chest CT in pediatric patients with high-risk neuroblastoma.

PROCEDURE

Medical records and imaging from 88 patients with high-risk neuroblastoma, diagnosed at St. Jude Children's Research Hospital between January, 2002 and December, 2009, were reviewed. Surveillance imaging was conducted through 2013. Ten patients with thoracic disease at diagnosis were excluded. Event free survival (EFS) and overall survival (OS) were estimated. Size specific dose estimates for CT scans of the chest, abdomen, and pelvis were used to estimate absolute organ doses to 23 organs. Organ dosimetry was used to calculate cohort effective dose.

RESULTS

The 5 year OS and EFS were 51.9% ± 6.5% and 42.6% ± 6.5%, respectively. Forty-six (58.9%) patients progressed/recurred and 41 (52.6%) died of disease. Eleven patients (14%) developed thoracic disease progression/recurrence identified by chest CT (1 paraspinal mass, 1 pulmonary nodules, and 9 nodal). MIBG (metaiodobenzylguanidine) scans identified thoracic disease in six patients. Five of the 11 had normal chest MIBG scans; three were symptomatic and two were asymptomatic with normal chest MIBG scans but avid bone disease. The estimated radiation dose savings from surveillance without CT chest imaging was 42%, 34% when accounting for modern CT acquisition (2011-2013).

CONCLUSIONS

Neuroblastoma progression/recurrence in the chest is rare and often presents with symptoms or is identified using standard non-CT imaging modalities. For patients with non-thoracic high-risk neuroblastoma at diagnosis, omission of surveillance chest CT imaging can save 35-42% of the radiation burden without compromising disease detection.

Development and characterization of a human orthotopic neuroblastoma xenograft

Neuroblastoma is a pediatric cancer of the developing sympathoadrenal lineage. The tumors are known to develop from the adrenal gland or paraspinal ganglia and have molecular and cellular features of sympathetic neurons such as dense core vesicles and catecholamine production. Here we present the detailed molecular, cellular, genetic and epigenetic characterization of an orthotopic xenograft derived from a high-risk stage 4 neuroblastoma patient. Overall, the xenografted tumor retained the high risk features of the primary tumor and showed aggressive growth and metastasis in the mouse. Also, the genome was preserved with no additional copy number variations, structural variations or aneuploidy. There were 13 missense mutations identified in the xenograft that were not present in the patient's primary tumor and there were no new nonsense mutations. None of the missense mutations acquired in the xenograft were in known cancer genes. We also demonstrate the feasibility of using the orthotopic neuroblastoma xenograft to test standard of care chemotherapy and molecular targeted therapeutics. Finally, we optimized a new approach to produce primary cultures of the neuroblastoma xenografts for high-throughput drug screening which can be used to test new combinations of therapeutic agents for neuroblastoma.

Genomic landscape of paediatric adrenocortical tumours

Pediatric adrenocortical carcinoma is a rare malignancy with poor prognosis. Here we analyze 37 adrenocortical tumors (ACTs) by whole genome, whole exome and/or transcriptome sequencing. Most cases (91%) show loss of heterozygosity (LOH) of chromosome 11p, with uniform selection against the maternal chromosome. IGF2 on chromosome 11p is overexpressed in 100% of the tumors. TP53 mutations and chromosome 17 LOH with selection against wild-type TP53 are observed in 28 ACTs (76%). Chromosomes 11p and 17 undergo copy-neutral LOH early during tumorigenesis, suggesting tumor-driver events. Additional genetic alterations include recurrent somatic mutations in ATRX and CTNNB1 and integration of human herpesvirus-6 in chromosome 11p. A dismal outcome is predicted by concomitant TP53 and ATRX mutations and associated genomic abnormalities, including massive structural variations and frequent background mutations. Collectively, these findings demonstrate the nature, timing and potential prognostic significance of key genetic alterations in pediatric ACT and outline a hypothetical model of pediatric adrenocortical tumorigenesis.

Pediatric solid tumor genomics and developmental pliancy

Pediatric solid tumors are remarkably diverse in their cellular origins, developmental timing and clinical features. Over the last 5 years, there have been significant advances in our understanding of the genetic lesions that contribute to the initiation and progression of pediatric solid tumors. To date, over 1000 pediatric solid tumors have been analyzed by Next-Generation Sequencing. These genomic data provide the foundation to launch new research efforts to address one of the fundamental questions in cancer biology—why are some cells more susceptible to malignant transformation by particular genetic lesions at discrete developmental stages than others? Because of their developmental, molecular, cellular and genetic diversity, pediatric solid tumors provide an ideal platform to begin to answer this question. In this review, we highlight the diversity of pediatric solid tumors and provide a new framework for studying the cellular and developmental origins of pediatric cancer. We also introduce a new unifying concept called cellular pliancy as a possible explanation for susceptibility to cancer and the developmental origins of pediatric solid tumors.

Targeting the DNA repair pathway in Ewing sarcoma

Ewing sarcoma (EWS) is a tumor of the bone and soft tissue that primarily affects adolescents and young adults. With current therapies, 70% of patients with localized disease survive, but patients with metastatic or recurrent disease have a poor outcome. We found that EWS cell lines are defective in DNA break repair and are sensitive to PARP inhibitors (PARPis). PARPi-induced cytotoxicity in EWS cells was 10- to 1,000-fold higher after administration of the DNA-damaging agents irinotecan or temozolomide. We developed an orthotopic EWS mouse model and performed pharmacokinetic and pharmacodynamic studies using three different PARPis that are in clinical development for pediatric cancer. Irinotecan administered on a low-dose, protracted schedule previously optimized for pediatric patients was an effective DNA-damaging agent when combined with PARPis; it was also better tolerated than combinations with temozolomide. Combining PARPis with irinotecan and temozolomide gave complete and durable responses in more than 80% of the mice.

Recurrent somatic structural variations contribute to tumorigenesis in pediatric osteosarcoma

Pediatric osteosarcoma is characterized by multiple somatic chromosomal lesions, including structural variations (SVs) and copy number alterations (CNAs). To define the landscape of somatic mutations in pediatric osteosarcoma, we performed whole-genome sequencing of DNA from 20 osteosarcoma tumor samples and matched normal tissue in a discovery cohort, as well as 14 samples in a validation cohort. Single-nucleotide variations (SNVs) exhibited a pattern of localized hypermutation called kataegis in 50% of the tumors. We identified p53 pathway lesions in all tumors in the discovery cohort, nine of which were translocations in the first intron of the TP53 gene. Beyond TP53, the RB1, ATRX, and DLG2 genes showed recurrent somatic alterations in 29%-53% of the tumors. These data highlight the power of whole-genome sequencing for identifying recurrent somatic alterations in cancer genomes that may be missed using other methods.

Targeting oxidative stress in embryonal rhabdomyosarcoma

Rhabdomyosarcoma is a soft-tissue sarcoma with molecular and cellular features of developing skeletal muscle. Rhabdomyosarcoma has two major histologic subtypes, embryonal and alveolar, each with distinct clinical, molecular, and genetic features. Genomic analysis shows that embryonal tumors have more structural and copy number variations than alveolar tumors. Mutations in the RAS/NF1 pathway are significantly associated with intermediate- and high-risk embryonal rhabdomyosarcomas (ERMS). In contrast, alveolar rhabdomyosarcomas (ARMS) have fewer genetic lesions overall and no known recurrently mutated cancer consensus genes. To identify therapeutics for ERMS, we developed and characterized orthotopic xenografts of tumors that were sequenced in our study. High-throughput screening of primary cultures derived from those xenografts identified oxidative stress as a pathway of therapeutic relevance for ERMS.

CTNNB1 genotyping and APC screening in pediatric desmoid tumors: a proposed algorithm

Desmoid fibromatosis is a rare, locally aggressive fibroblastic/myofibroblastic tumor that occasionally involves children. We examined a series of pediatric desmoids for CTNNB1 mutations, seen in sporadic tumors, and APC germline mutations, associated with familial adenomatous polyposis (FAP). Forty-four desmoids in pediatric patients were identified in the pathology files of 2 large referral centers (1995-2009). Clinical charts were reviewed for history of FAP. Germline APC gene mutations were determined on blood samples from patients presenting with FAP. Immunohistochemistry for beta-catenin was performed. CTNNB1 genotyping was done by Sanger sequencing on formalin-fixed paraffin-embedded tissue. CTNNB1 mutations were observed in 29 of 44 (66%) desmoids, with 3 mutations identified: T41A (64%), S45F (29%), and S45P (7%). Germline APC mutations were present in 7 (16%) desmoid patients. Eight (18%) patients had desmoids that were wild type for CTNNB1 and had no known clinical signs or family history suspicious for FAP at the time of testing or with extended follow up (n  =  6). Beta-catenin nuclear labeling was observed in 38 of 41 (92%) tested cases, 34 (89%) of which showed mutations in either CTNNB1 (n  =  29) or APC (n  =  5). Nuclear localization of beta-catenin was seen in the majority of pediatric desmoids and was most often associated with somatic mutations in CTNNB1. However, a significant proportion of pediatric patients harbored germline mutations in APC. Given the implications, genetic counseling is recommended for children diagnosed with desmoid tumors lacking CTNNB1 mutations because this population is enriched for FAP patients.

A phase 2 trial of trabectedin in children with recurrent rhabdomyosarcoma, Ewing sarcoma and non-rhabdomyosarcoma soft tissue sarcomas: a report from the Children's Oncology Group

PURPOSE

To determine the toxicity, efficacy and pharmacokinetics of trabectedin given over 24h every 3 weeks to children with recurrent rhabdomyosarcoma, Ewing sarcoma, or non-rhabdomyosarcoma soft tissue sarcomas.

PATIENTS AND METHODS

Trabectedin was administered as a 24-h intravenous infusion every 21 days. Two dose levels were evaluated (1.3 and 1.5mg/m(2)) for safety; efficacy was then evaluated using a traditional 2-stage design (10+10) at the 1.5mg/m(2) dose level. Pharmacokinetics (day 1 and steady state) were performed during cycle 1.

RESULTS

Fifty patients were enrolled, eight patients at 1.3mg/m(2) and 42 at 1.5mg/m(2). Dose limiting toxicities (DLTs) in the dose finding component included fatigue and reversible GGT elevation in 1/6 evaluable patients at 1.3mg/m(2) and 0/5 at 1.5mg/m(2). Efficacy was evaluated in 42 patients enrolled at the 1.5mg/m(2) dose of whom 22% experienced reversible grade 3 or 4 toxicities that included AST, ALT, or GGT elevations, myelosuppression and deep venous thrombosis. One patient with rhabdomyosarcoma had a partial response and one patient each with rhabdomyosarcoma, spindle cell sarcoma and Ewing sarcoma had stable disease for 2, 3 and 15 cycles, respectively.

CONCLUSION

Trabectedin is safe when administered over 24h at 1.5mg/m(2). Trabectedin did not demonstrate sufficient activity as a single agent for children with relapsed paediatric sarcomas.

Clinical outcome of children and adults with localized Ewing sarcoma: impact of chemotherapy dose and timing of local therapy

BACKGROUND

As Ewing sarcoma (EWS) can affect children and adults, these patients can be treated at either a pediatric or an adult institution. This study investigated whether differences in therapeutic strategy undertaken in pediatric and adult specialty sarcoma centers correlated with clinical outcome.

METHODS

Data from patients with localized EWS treated between 1990 and 2005 at tertiary care pediatric and adult institutions were reviewed.

RESULTS

Fifty-three patients (24 adult and 29 pediatric) were treated. Pediatric patients received a median of 16 cycles of chemotherapy comprised of doxorubicin, vincristine, cyclophosphamide, ifosfamide, and etoposide. Adult patients received a median of 10 cycles of treatment, and a significantly lower total cumulative dose of ifosfamide and cyclophosphamide (P < .0001). There was no difference noted with regard to the total dose of doxorubicin, or in the type of local therapy offered (surgery or radiotherapy, vs both). However, local therapy occurred earlier in pediatric patients compared with adults (3.7 months vs 7.4 months; P = .0003). The 3-year event-free survival (EFS) rate in pediatric and adult patients was 70% +/- 9% and 43% +/- 13% (P = 0.1), respectively. The 3-year overall survival rate was 81% +/- 7.7% and 59% +/- 12% (P = .02) for pediatric and adult patients, respectively. Factors found to be significantly associated with EFS on univariate analysis included pelvic site, cyclophosphamide dose, and time to local therapy. On multivariate analysis, only pelvic disease (hazard ratio [HR] 4.26; P = .018) and time to local therapy (HR, 1.19; P = .002) were found to be significant.

CONCLUSIONS

Adults with localized EWS have an inferior outcome compared with pediatric patients. This difference may be related to lower doses of alkylating agents and the timing of local therapy.

Amifostine does not prevent platinum-induced hearing loss associated with the treatment of children with hepatoblastoma: a report of the Intergroup Hepatoblastoma Study P9645 as a part of the Children's Oncology Group

BACKGROUND

The current study was conducted to determine whether amifostine is effective in reducing the toxicities associated with the administration of platinum-containing regimens in children with hepatoblastoma (HB).

METHODS

Patients were enrolled on P9645 beginning in March of 1999. Patients who had stage I/II disease received treatment with 4 cycles of combined cisplatin, 5-fluorouracil, and vincristine (C5V) with or without amifostine. Patients who had stage III/IV disease were randomized to receive treatment with 6 cycles of either C5V with or without amifostine or carboplatin alternating with cisplatin (CC) with or without amifostine. Patients who were randomized to receive amifostine were given a dose of 740 mg/m2 intravenously over 15 minutes before each administration of a platinum agent.

RESULTS

Eighty-two patients were considered in a special interim analysis of the incidence of toxicity. The disease outcome for patients who received amifostine was similar to the outcome for patients who did not receive amifostine (P=.22). The incidence of significant hearing loss (>40 dB) was similar for patients who did or did not receive amifostine (38% [14 of 37 patients] vs 38% [17 of 45 patients], respectively; P=.68). There were no differences in the incidence of renal or bone marrow toxicities evaluated. Patients who received amifostine had a higher incidence of hypocalcemia (5% vs 0.5%; P=.00006).

CONCLUSIONS

Amifostine in the doses and schedule used in this study failed to significantly reduce the incidence of platinum-induced toxicities in patients with HB.

Alveolar rhabdomyosarcoma of the extremity and nodal metastasis: Is the in-transit lymphatic system at risk?

Alveolar rhabdomyosarcoma (RMS) of the extremity is not infrequently associated with regional node metastasis. Knowledge of lymphatic drainage of extremity RMSs is important to determine radiotherapy fields. In this report we describe two patients with alveolar RMS of the lower extremity with inguinal metastasis at presentation. Both the distal lower extremity and inguinal region received local therapy consisting of surgery and postoperative radiotherapy. Both patients later developed in-transit lymphatic metastasis outside of the irradiated field. The in-transit lymphatics can be a site of failure in children with alveolar RMS of the extremity and nodal involvement.