Primary intratesticular rhabdomyosarcoma (PITRMS) is an exceptionally rare and aggressive tumor, arising from mesenchymal cells with rhabdomyoblastic differentiation. Rhabdomyosarcoma accounts for 3% of adult soft tissue sarcomas and is most common in children, often seen in the bladder and paratesticular regions. Only 24 cases of PITRMS have been reported worldwide (Abdikarin et al., 2024), with no known cases previously documented in the Philippines.

We present the 1st reported case in the Philippines of PITRMS in a 14-year-old male with abdominopelvic and brain metastases. This exceptionally rare malignancy highlights the need for greater awareness, as not all testicular masses share the same prognosis. PITRMS is significantly more aggressive than non-seminomatous germ cell tumors and requires a different therapeutic approach due to its distinct behavior and poor response to standard chemotherapy and radiotherapy.

A 14 y.o male presented with a painless, progressively enlarging left scrotal mass over 12 months. On PE, a non-tender, non-transilluminating mass was palpated. A scrotal ultrasound revealed a 11.6 x 5.2 x 4.7 cm (149 ml) predominantly solid mass in the left hemiscrotal sac, suggestive of testicular new growth. Tumor markers were normal. WA Ultrasound was done with noted multiple enlarged lymph nodes in the paraaortic area with an average diameter of 1.0 cm, suspicious of metastatic adenopathy. Pre-op diagnosis was Testicular Mass, Left, to consider Non-Seminomatous Germ Cell Carcinoma, Left, Stage IIA (cT1bN1M0S0). Radical orchiectomy, Left was performed. Histopathology results noted (+) malignant spindle neoplasm favor intra-testicular rhabdomyosarcoma, (+) tumor involvement, tunica albuginea, tunica vaginalis, (-) tumor involvement, spermatic cord. Microsections of the mass reveal (+) malignant neoplasm composed of cells predominantly in loose myxoid stroma with histomorphologically unremarkable seminiferous tubules and epididymis with normal ducts and surrounding muscle layer. Immunohistochemistry results noted features supporting the diagnosis of Embryonal Rhabdomyosarcoma with (+) Desmin, (+) Myogenin. Post-op diagnosis was Primary Intratesticular Embryonal Rhabdomyosarcoma, Left, Stage IV (pT3N1M0), patient was then advised chemotherapy but was lost to follow-up. He returned two months later with abdominopelvic pain and a large 28.7 cm mass. Cranial plain CT scan revealed multiple brain lesions. He was re-staged to Stage IV (pT4N1M1). High-risk rhabdomyosarcoma protocol was initiated. By week 32, patient had complete response of the target lesion (intra-abdominal mass), however with a non-complete response of the non-target lesion (left inguinal region). A total of 28 fractions of EBRT (50.4 Gy) to the left inguinal area was done. Re-evaluation CT showed a residual enhancing mass inseparable from the left rectus abdominis. Currently, the patient is ECOG 0 and Karnofsky 100%, and is continuing his 54-week chemotherapy protocol.

This is the 1st reported case of PITRMS in the Philippines. It highlights the need to consider rare malignancies when evaluating testicular masses, as PITRMS differs significantly from GCTs in prognosis and management, requiring a multidisciplinary approach involving surgery, chemotherapy, and radiotherapy.