Poor outcome in congenital mesoblastic nephroma with TPM3::NTRK1 fusion: a case report from multi-disciplinary treatment to molecular tumor board.

Background: Congenital mesoblastic nephroma (CMN) is a rare renal tumor with good prognosis in children; however, cellular CMN is a special subtype with poor prognosis. The ETV6 fusion gene has been found in some cellular CMNs, whereas CMNs with TPM3::NTRK1 fusion gene have not been reported. This study aims to share the progression and treatment of a case of CMNs with TPM3::NTRK1 fusion gene, in order to provide experience for the diagnosis and treatment of such specific diseases.

Case description: We report a case of CMN with TPM3::NTRK1 fusion gene and a 3-year course of disease that originated during the fetal period. The child experienced rapid tumor progression 22 months after birth, followed by tumor recurrence 3 months after complete resection of CMN. Although traditional chemotherapy could not prevent the tumor progression. The tropomyosin receptor kinase (TRK) inhibitor larotrectinib resulted in significant inhibitory effects on metastatic lesions in the lungs, liver, and peritoneum. However, the patient ultimately died as the tumor became resistant to larotrectinib.

Conclusions: CMN, is a rare pediatric renal tumor that warrant prompt surgical management. A watchful waiting approach may allow for aggressive growth of metastatic disease, as seen in this case of cellular CMN with TPM3::NTRK1 fusion gene, TRK inhibitors can play significant roles in the treatment of CMN with TPM3::NTRK1 fusion gene, but we still need to pay attention to the phenomenon of drug resistance to larotrectinib caused by site mutations of TRKA.