Brachytherapy Represents a Potential Strategy in AYA Patients With Rhabdomyosarcoma

Sara J. Zakem, MD

Although brachytherapy (BT) is rarely utilized as a treatment for pediatric and adolescent/young adult (AYA) patients in the United States, AYA patients with rhabdomyosarcoma (RMS) treated with BT had favorable survival outcomes, according to findings from a study published in Pediatric Blood & Cancer.¹

Survival data were available for 31 of 37 patients with RMS who were treated with BT. At a median follow-up of 63 months, the overall survival (OS) rate was 100% in patients who had a favorable primary site vs 54% at a median follow-up of 42 months in patients with unfavorable primary sites (P < .027).

“[This suggests] that this approach may not compromise oncologic outcomes and warrants further study as a therapeutic option in pediatric and AYA patients, specifically in RMS,” lead study author Sara J. Zakem, MD, a clinical assistant professor in the Department of Radiation Oncology at the Seattle Cancer Care Alliance Peninsula and University of Washington Medicine, and coauthors wrote.

AYA patients with solid tumors are typically treated with a multimodality approach of surgery, chemotherapy, and radiation therapy. Although this strategy has improved outcomes, late toxicities remain a challenge.

BT can deliver highly conformal radiation therapy to patients that spares surrounding tissue. In turn, this can limit short- and long-term effects of radiation therapy, like acute myelosuppression, late effects on growth, and risk of secondary malignancy, in AYA patient populations.

Moreover, BT is given over a shortened treatment interval compared with external beam radiation therapy (EBRT), which may make BT more feasible for younger patients and their families.

The study was developed to characterize trends in BT use among AYA patients based in the United States, particularly those with RMS.

Disease, treatment, and outcome data of patients 21 years of age or younger who were treated for solid tumor malignancies were collected retrospectively from the deidentified National Cancer Database. Patients were treated in the United States from 2004 to 2016.

In total, 99506 pediatric and AYA patients were included in the study. Of these, 23% (n = 22586) received radiation therapy with EBRT and or BT and 0.2% (n = 240) received BT. Of the patients treated with BT, more than half (57.9%; n = 139) underwent surgery and 24.2% (n = 58) received EBRT.

Of the patients treated with BT, tumor types included sarcoma (n = 74), melanoma (n = 54), squamous cell carcinoma (SCC; n = 31), retinoblastoma (n = 24), clear cell/adenocarcinoma (n = 23), and other histologies (n = 34). The majority of patients were female (68.3%) and White (78.3%) and were a median of 16 years of age (range, 0-21). Most patients had private insurance (60.8%).

Regarding BT type, 27.5% of patients received high-dose rate (HDR) intracavitary BT, 21.3% received HDR interstitial BT, 6.7% received low-dose rate (LDR) intracavitary BT, 11.7% received LDR interstitial BT, and 32.9% received an unknown type of BT.

Approximately 3.8% (n = 3836) of all patients were treated for RMS. Of this population, two-thirds (66%; n = 2531) received any radiation therapy and 1% (n = 37) received BT.

Of the patients with RMS who received BT, 26 had embryonal disease and 11 had alveolar disease. Most patients were female (73%; n = 27) and White (78.3%; n = 29) and were a median of 4 years of age (range, 0-16). Primary sites of disease included the prostate (5.4%; n = 2), retroperitoneum (8.1%; n = 3), skin (2.7%; n = 1), soft palate (5.4%; n = 2), soft tissue (45.9%; n = 17), uterus/vagina/vulva (32.4%; n = 12).

Moreover, 3 received BT plus EBRT whereas the other 34 patients received BT alone. Additionally, most patients treated for RMS underwent surgery in addition to BT (n = 75.7%; n = 28). Most patients (62.1%; n = 23) underwent radiation after surgery. Types of BT included HDR intracavitary (35.1%; n =13), HDR interstitial (27%; n = 10), LDR intracavitary (2.7%; n = 1), and unknown (35.1%; n = 13). 

Additional survival data showed that at a median follow-up of 61 months, the median OS was undefined for all histologies. Patients with retinoblastoma has the best OS rate at 100% at 5 years, whereas patients with SCC had a 5-year OS rate of 72% (P < .008).

For the patients with RMS and available survival data, the median OS was undefined for all patients and for the subset of patients with embryonal RMS at a median follow-up of 46 months. The median OS was 71 months in patients with alveolar RMS. 

For patients with RMS of the uterus/vagina/vulva the OS rate was 100% at a median follow-up of 19 months, but median OS was undefined for this group of patients.

“We believe that future collaboration with our international colleagues, both to learn from their robust clinical experience and to form an international consortium for research is an important step for demonstrating the value of and improving access to BT in the United States,” concluded the study authors.

Reference

1. Zakem SJ, Cost CR, Cost NG, et al. Brachytherapy in children, adolescents, and young adults: an underutilized modality in the United States? Pediatr Blood Cancer. 2022;69(3):e29412. doi:10.1002/pbc.29412