Embryonal rhabdomyosarcoma of the prostate in adults: rare location and diagnostic pitfalls in a case report

Introduction

Rhabdomyosarcoma (RMS) is a group of malignant mesenchymal tumors most commonly seen in children, with the genitourinary system affected in approximately 20% of cases (1). RMS can be classified into three main subtypes: embryonal, alveolar, pleomorphic, and sclerosing (2). Embryonal RMS (ERMS) of the prostate is an exceptionally rare malignancy in adults, accounting for less than 1% of all prostate cancers (3).

To date, only twenty cases of ERMS of the prostate have been documented in the literature (4-9). This aggressive tumor is characterized by rapid local growth, emphasizing the need for prompt diagnosis (10). Definitive diagnosis relies on histological features and immunohistochemical studies. Due to its nonspecific symptoms (11), it can easily be misdiagnosed as prostate adenocarcinoma, potentially leading to delayed treatment.

Here, we report the case of a 23-year-old male who presented to the emergency department with a pelvic mass and bilateral lower back pain, highlighting the rarity of this condition and the diagnostic challenges it poses in distinguishing between adenocarcinoma and RMS. We present this case in accordance with the CARE reporting checklist (available at https://jxym.amegroups.com/article/view/10.21037/jxym-24-79/rc).

Case presentation

A 23-year-old Arabian male presented with a 15-day history of bilateral lower back pain, dysuria, and bone pain, with no notable personal or family medical history. Digital rectal examination revealed an enlarged, firm prostate. Ultrasound of the urinary tract demonstrated a heterogeneous, enlarged prostate with bilateral ureterohydronephrosis. The total prostate-specific antigen (PSA) level was 0.35 ng/mL, which is within the normal range (i.e., less than 4 ng/mL). Multiparametric magnetic resonance imaging (MRI) revealed a heterogeneous, enhancing prostatic mass measuring 11.6 cm × 8.7 cm × 8 cm (Figure 1), infiltrating the posterior bladder wall, seminal vesicles, mesorectal fat, anterior rectal wall, and right psoas muscle (Figure 2). Additional findings included retroperitoneal, lumbo-aortic, and pelvic lymphadenopathy, as well as metastatic bone lesions (Figure 3). An outside pathologist initially diagnosed a prostate biopsy as Gleason grade 10 (5+5) prostatic adenocarcinoma. However, given the patient’s young age and low PSA level, the clinical team questioned this diagnosis and sought a second opinion in our pathology department. Histological review revealed a tumor with solid architecture composed of small cells featuring round or oval nuclei, marked anisokaryosis, inconspicuous nucleoli, and scant cytoplasm (Figure 4). Immunohistochemical staining showed positivity for anti-desmin and anti-myogenin, while anti-AE1/AE3 pancytokeratin was negative (Figure 5). These findings confirmed a diagnosis of ERMS. The patient underwent bilateral nephrostomy to relieve urinary obstruction. A multidisciplinary team initiated chemotherapy with doxorubicin (50 mg/m²), vincristine (2 mg), and ifosfamide (1.5 g/m²), administered every three weeks. After six cycles, a follow-up scan showed a partial response. Nevertheless, the patient succumbed to the disease eight months after the initiation of treatment, due to its advanced stage at the time of diagnosis. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Figure 1 Axial prostatic-MRI. (A) It shows an extensive prostatic mass (orange arrow) with an intermediate signal and small cystic area (yellow arrow) on T2-weighted sequences, (B) homogeneous hyposignal in T1-weighted images (orange arrow), and (C) heterogeneously enhanced (orange and yellow arrows) after gadolinium injection. (D,E) The arrow shows a high signal in DWI with low ADC value. ADC, apparent diffusion coefficient; DWI, diffusion weighted imaging; MRI, magnetic resonance imaging.

Figure 2 Prostatic MRI in sagittal T2-weighted images (A), after gadolinium injection (B), and in axial plan (C), showing the massive infiltration of the bladder and prevesical space (blue arrows), but also the seminal vesicles (green arrows), the mesorectum and the anterior wall of the rectum (yellow arrows). MRI, magnetic resonance imaging.

Figure 3 Prostatic MRI in axial T2-weighted sequence (A,B,D) and DWI sequence (C,E), showing infiltration of the right psoas muscle (green arrows), and infiltrative retroperitoneal, latero-aortic and iliac adenopathy (blue arrows). There were also two metastatic lesions in the right sacral wing and vertebral body of L1 (yellow arrows). DWI, diffusion weighted imaging; MRI, magnetic resonance imaging.

Figure 4 H&E stained image showing sheets of cells round with eosinophilic cytoplasm and hyperchromatic nuclei without prominent nucleolus, at 20× magnification. H&E, hematoxylin and eosin.

Figure 5 Immunochemistry 20× image showing desmin positivity (A) and myogenin positivity (B).

Discussion

ERMS most commonly arises in the paratesticular soft tissues, head and neck, extremities, and genitourinary tract (12,13). While frequent in infants and children—typically diagnosed around age five—it is exceptionally rare in adults, with only twenty reported cases in the literature (4-9). This case highlights the histopathological limitations and underlines the importance of immunohistochemical studies for accurate and early diagnosis, which is essential for improving prognosis.

Clinically, prostatic RMS presents with nonspecific genitourinary symptoms in its early stages, such as dysuria, urinary retention, and lower abdominal pain (11). Its aggressive nature drives rapid local growth (10).

MRI remains the modality of choice for defining the primary site of the sarcoma, its local extension, and the presence of regional lymphadenopathy, in addition to aiding in surgical planning. Most often, prostatic sarcoma appears as a homogenous T1 hypointense mass, heterogenous intermediate T2 signal, sometimes with areas of necrosis or cystic degeneration indicative of rapid growth and malignancy. Regarding diffusion, it may vary depending on the histological variant, with diffusion hyperintensity and a low apparent diffusion coefficient (ADC) value. Upon injection, these tumors may show intense or heterogeneous peripheral enhancement, reflecting the heterogeneous histological nature of the lesion, which can be solid or mixed. MRI could also help differentiate prostatic sarcoma from adenocarcinoma. In fact, apart from the signal characteristics of sarcomas, these tumors tend to extend beyond the prostate with local invasion of adjacent structures most often, whereas the majority of prostatic adenocarcinomas are confined to the prostate at the time of diagnosis. These are poorly defined and infiltrative tumors, sometimes well-limited with a pseudocapsule and displacing adjacent organs. Meanwhile, adenocarcinoma tends to infiltrate adjacent structures (14). Prostatic acid phosphatase and PSA levels are typically normal in RMS cases (15).

Diagnosis is established via transrectal needle biopsy, transurethral resection, or perineal biopsy. Tumor cells often exhibit excentric eosinophilic granular cytoplasm rich in thick and thin filaments, with variable shapes including round, elongated, strap-like, or tadpole-like cells. RMS encompasses several histologic subtypes—embryonal, botryoid, spindle cell (leiomyomatous), sclerosing, alveolar, and sarcoma not otherwise specified (NOS)—each with distinct prognostic and therapeutic implications. ERMS typically displays variable cellularity, with rhabdomyoblasts arranged in sheets and large nests within a myxoid matrix (16).

Few publications have addressed the diagnostic difficulties of prostatic RMS in adults (1,11,17); however, this report highlights its histological similarity to prostate adenocarcinoma, Gleason grade 10 (5+5), and other small round cell tumors.

Immunohistochemical testing is pivotal, showing positivity for desmin, myogenin, and myogenic differentiation 1 (MyoD1) (18), and negativity for epithelial and neuroendocrine markers. Differential diagnoses include prostatic small cell carcinoma, lymphoma, stromal sarcoma, sarcomatoid carcinoma (with RMS components), leiomyosarcoma, inflammatory myofibroblastic tumors, malignant peripheral nerve sheath tumors, and, rarely, rectal gastrointestinal stromal tumors (1,19).

In pediatric patients, ERMS generally carries a favorable prognosis, even in uncommon sites like the prostate or bladder. Conversely, in adults, prostatic ERMS is associated with an aggressive course and poor prognosis, with a 5-year survival rate of 27% for all adult RMSs, compared to 61% in children (3). The reasons for this disparity remain unclear. The tumor often involves regional lymph nodes and distant metastases, particularly to the lungs and bones, with over 25% of adult prostatic ERMS cases presenting with metastases at diagnosis (13).

Treatment is multimodal, combining surgery, radiotherapy, and chemotherapy, and is adapted to the stage of the disease. In cases of localized disease, radical prostatectomy with pelvic lymph node dissection is preferred (20). Radiotherapy is used as an adjunct in the presence of high-risk features, such as positive margins or extraprostatic extension. Chemotherapy is essential in advanced or metastatic cases (21), such as in our patient. The combination of vincristine, actinomycin D, and cyclophosphamide (VAC regimen) is still considered the standard chemotherapy protocol for ERMS (22). Given the highly aggressive nature of this tumor, the patient died eight months after the initiation of treatment.

Conclusions

Prostatic RMS is an extremely rare malignancy in adults with a generally poor prognosis compared to pediatric cases. Precise histologic subtyping is crucial for guiding treatment and improving outcomes. This case illustrates the value of seeking a second pathological opinion to ensure diagnostic accuracy.

Acknowledgments

We would like to thank Dr. Kamil Ali Mohamed from the Department of Pathology, Ibn Sina Hospital, Rue Lamfadel Cherkaoui—Institute B.P 6527, Rabat, Morocco, for his help in polishing our paper.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://jxym.amegroups.com/article/view/10.21037/jxym-24-79/rc

Peer Review File: Available at https://jxym.amegroups.com/article/view/10.21037/jxym-24-79/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jxym.amegroups.com/article/view/10.21037/jxym-24-79/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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