Gastric cancer cells may infiltrate through the retroperitoneal space along the spermatic cord sheath or adjacent tissues. Hanash et al. (4) proposed that embryonic remnants (e.g., the processus vaginalis) could provide anatomical conduits for tumor cell descent.

Evidence suggests overlapping lymphatic metastatic pathways between testicular and gastric malignancies. When gastric carcinoma cells obstruct the thoracic duct, the resultant retrograde lymphatic flow may facilitate tumor cell dissemination to the scrotum via the cisterna chyli and genitourinary lymphatic trunks (19).Yao et al. (5) demonstrated that approximately 30% of cutaneous metastases are associated with lymphatic dissemination, particularly when the retroperitoneal lymphatic chain is involved, allowing tumor cells to extend into the spermatic cord. Kageyama et al. (10) reported a case of gastric cancer metastasis via lymphovascular tumor thrombi within the spermatic cord, providing histopathological evidence supporting this mechanism.

The blood supply and drainage of the spermatic cord are achieved through the coordinated function of arterial and venous systems. In the arterial system: The testicular artery, originating directly from the abdominal aorta, descends along the spermatic cord into the scrotum and is primarily responsible for oxygenated blood delivery to the testes and epididymis. The deferential artery, arising from the superior vesical artery, courses along the ductus deferens to supply surrounding tissues. The cremasteric artery, originating from the inferior epigastric artery, distributes to the cremaster muscle and external spermatic fascia, contributing to testicular positional regulation. The venous system centers around the pampiniform plexus - a plexiform network formed by a dense network of extensively anastomosing small veins that encircle the testicular artery, facilitating thermoregulation and venous return (20). Tas et al. (6) reported a case of gastric cancer with concurrent multifocal metastases to the scrotum and facial skin, providing clinical evidence supporting the plausibility of hematogenous spread.

When peritoneal metastatic lesions are located near the root of the spermatic cord, tumor cells may infiltrate the spermatic cord through local invasion. Sekita et al. (9) intraoperatively observed adhesive lesions between the peritoneum and spermatic cord, providing direct pathological evidence supporting this mechanism.

In the present case, radiographic and intraoperative findings ruled out direct invasion or peritoneal seeding. Notably, the patient had a history of peritoneal metastasis in 2022, which may have established a pre-existing lymphatic pathway for tumor dissemination. Park et al. (18) demonstrated that retroperitoneal lymphatic trunks connecting the peritoneum and spermatic cord could facilitate retrograde lymphatic spread even after peritoneal lesions regress. Residual tumor cells from prior peritoneal metastasis might have migrated along these pathways, bypassing the need for active peritoneal involvement at the time of scrotal metastasis. This hypothesis aligns with the proposed mechanism of retrograde lymphatic dissemination via the thoracic duct or genitourinary lymphatic trunks (5, 10).However, definitive evidence, such as the identification of lymphovascular tumor emboli, is required to solidify this conclusion.

This finding underscores the necessity for surgeons to maintain heightened vigilance for spermatic cord or scrotal lesions during long-term postoperative follow-up. We recommend incorporating scrotal ultrasound into routine follow-up protocols for gastric cancer patients and emphasize the importance of pathological evaluation for scrotal masses of unknown etiology. The clinical manifestation of scrotal skin metastasis is typically a painless nodule or mass without specific morphological features, making it difficult to distinguish from other benign lesions, such as sebaceous cysts, abscesses, or localized infections (11). Therefore, imaging evaluation and histopathological examination are crucial for diagnosis. Scrotal ultrasound is often the preferred imaging modality for scrotal lesions due to its high resolution and non-invasiveness, effectively differentiating abnormalities in subcutaneous tissues from testicular parenchyma. However, ultrasound has limitations in distinguishing primary malignancies from metastatic lesions, and final diagnosis relies on pathological examination and immunohistochemical markers (12). In this patient, immunohistochemical analysis showed positive expression for CK20, CK7, and CDX-2, strongly supporting the diagnosis of scrotal metastasis from gastric adenocarcinoma.

The prognosis for patients with cutaneous metastases is generally poor, especially for those with widespread visceral metastases. The median survival for gastric cancer patients with skin metastasis is typically less than three months (13, 14). However, some patients have achieved long-term survival with aggressive treatment, including surgical resection, chemotherapy, targeted therapy, and immunotherapy (15, 16). In this case, next-generation sequencing (NGS) analysis identified KRAS p.G12V and TP53 splice-site mutations, indicating sustained activation of the MAPK signaling pathway and genomic instability (21). Although low expression of Claudin18.2 restricts targeted therapy options, MEK inhibitors targeting KRAS (e.g., trametinib) and WEE1 inhibitors addressing TP53 mutations (e.g., adavosertib) may synergistically overcome drug resistance (21, 22). The MSS status and low TMB suggest avoiding immune monotherapy, while combination with anti-angiogenic agents (e.g., Ramucirumab) may enhance immune microenvironment responsiveness. Future efforts should focus on dynamic monitoring of PD-L1 expression to guide precise therapeutic interventions in immunotherapy. The recent introduction of immune checkpoint inhibitors, such as PD-1/PD-L1 inhibitors, has markedly changed the treatment landscape for advanced gastric cancer. Studies indicate that immunotherapy shows substantial efficacy in patients with high PD-L1 expression, with some cases showing long-term remission (17). Future research should focus on exploring the applications of targeted and immunotherapies for advanced gastric cancer and its rare metastatic presentations to provide more treatment options and improve prognosis.