Background

Rhabdomyosarcoma, a malignant neoplasm arising from primitive mesenchymal cells, typically manifests in the skeletal muscles and can occur virtually anywhere in the body. Its most prevalent primary sites include the head and neck (approximately 50%), genitourinary tract (~ 25%), and extremities (~ 15%) [1]. The instances of rhabdomyosarcoma metastasizing to distant sites such as the breast highlight the aggressive behavior and potential for atypical dissemination of this tumor. Approximately 20% of rhabdomyosarcoma patients present with metastases at diagnosis, most commonly to the lungs, bone marrow, and lymph nodes [2].

Case presentation

A 20-year-old previously healthy female presented to our clinic with complaints of persistent left-hand swelling and discomfort. An initial assessment revealed a palpable mass in the left hand associated with localized pain. Regrettably, due to the urgency of the symptoms and the assumption of a possible benign etiology, surgical excision was performed without prior imaging evaluation. Postoperative histopathological analysis unexpectedly unveiled findings of a malignant spindle cell tumor. Approximately two months following the excision, the patient returned with alarming symptoms of rapidly growing bilateral breast masses associated with tenderness and skin changes. Imaging studies were initiated by ultrasound examination that revealed bilateral breast masses with heterogeneous characteristics. Notably, the retro-areolar region of the left breast exhibited a large, irregular soft tissue lesion, while smaller masses were observed in the contralateral breast. Moreover, bilateral axillary lymphadenopathy was evident on imaging, suggestive of potential metastatic involvement (Fig. 1).

Fig. 1
figure 1

Bilateral diagnostic ultrasound that shows a large heterogeneous soft tissue mass lesion seen at the retro-areolar region of the left breast (A), another smaller one seen at the right breast (B, C). All of them are anti-parallel orientation and do not respect related tissue plans. D Pathological left axillary LNs with a near total replacement of normal nodal tissue

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Further characterization through magnetic resonance imaging (MRI) confirmed the presence of malignant criteria within the bilateral breast masses. The left retro-areolar mass exhibited diffuse thickening of the overlying skin. Additionally, enlarged ipsilateral left axillary lymph nodes displayed total replacement by soft tissue, mirroring that in the left breast (Fig. 2).

Fig. 2
figure 2

Breast MRI axial plan post-contrast T1WI STIR A post-contrast T1WI B, C show large heterogeneously enhanced left retro-areolar mass lesion with diffuse thickening of the overlying skin, also enlarged bilateral axillary lymph nodes with the left-sided ones are seen replaced by soft tissue signal resampling that of left breast mass. Dynamic curve (D) on ROI on left breast mass shows a washout pattern curve

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To establish a definitive diagnosis, ultrasound-guided true-cut needle biopsies were performed of both breast masses. Histopathological examination, along with immunophenotyping, conclusively identified metastatic malignant spindle cell tumors consistent with rhabdomyosarcoma. This unexpected diagnosis underscored the need for comprehensive evaluation and heightened suspicion of metastatic disease in unusual presentations. Subsequent metastatic work-up, including contrast-enhanced CT scans, unveiled an extensive spread of the disease. Metastases were observed in various visceral sites, notably with findings of myocardial involvement, in addition to pulmonary nodules, nodal metastasis in mediastinal, hilar, and para-aortic regions, as well as hepatic metastatic deposits (Fig. 3).

Fig. 3
figure 3

Contrast-enhanced CT chest axial cuts on a mediastinal window that shows a well-defined hypodense focal mass lesion seen at the region of the inter-ventricular septum (a) and enlarged mediastinal, hilar, and left axillary lymph nodes as well as a large left breast mass (b). An axial cut of pulmonary widow shows few pulmonary nodules (c). An axial cut on the upper abdomen shows multiple hepatic focal lesions and enlarged amalgamated gastro-hepatic and porta-hepatis lymph nodes (d)

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Discussion

The occurrence of breast metastasis from rhabdomyosarcoma is an infrequent presentation, representing only a small fraction of metastatic cases. The literature primarily documents metastases to the lungs, bone marrow, and lymph nodes in rhabdomyosarcoma patients at diagnosis [3]. An unusual dissemination pattern was observed in this case, with the initial presentation in the hand followed by subsequent metastasis to the breasts. The identification of metastatic deposits in visceral organs, nodal regions, and even myocardial tissue further complicates the disease course and treatment approach [2]. This highlights the aggressive nature of rhabdomyosarcoma. Awareness among clinicians regarding the potential for breast metastasis in patients with primary rhabdomyosarcoma in other anatomical locations is crucial for prompt intervention and tailored management plans [2].

Conclusions

Metastasis of rhabdomyosarcoma to the breast is rare and occurs in young women as in our case with mainly primary site in limbs. It is important to be clinically aware of the risk of breast metastasis in female patients with primary extra-mammary rhabdomyosarcoma.