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case_images: Imaging findings upon Initial Diagnosis. (A, B) An array of minuscule pulmonary nodules (marked by the red arrows) aroused suspicions of metastasis within the lungs. (C, D) Computed Tomography (CT) scans, alongside Magnetic Resonance Imaging (MRI) (E, F), revealed the encroachment of a mass (marked by the red arrows) measuring 4.2 x 4.0 x 3.5cm at the inferior pole of the right kidney, encompassing the renal pelvis. .
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case_images: A 55-year-old man, was first admitted to Wuhan Bauhinia Hospital due to "painless gross hematuria for 3 months" and underwent "laparoscopic radical resection of right renal carcinoma " under general anesthesia on July 25, 2020 ( Figure 1 ).
case_images: Tumor specimen exhibiting histopathological characteristics consistent with thyroid follicular-like renal cell carcinoma (TLFRCC). Neoplastic cells displayed an assortment of thyroid follicular-like structures varying in size. The presence of fibrosis at the tumor core was accompanied by hyaline degeneration and localized ossification, as evidenced by histological examination (hematoxylin-eosin staining). Immunohistochemical (IHC) analysis revealed distinctive features of thyroid follicular renal cell carcinoma, characterized by positive expression of PAX8 and Vimentin, while the thyroid-specific markers thyroglobulin (TG) and thyroid transcription factor-1 (TTF-1) remained negative.
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case_images: It was initially revealed by Wuhan Asian Heart Hospital and verified by our entire pathology department through pathology consultation on July 5, 2023 ( Figure 2 ).
case_images: Showcases the occurrence of relapse, accompanied by a proliferation of lung metastatic nodules. (A, B) Myriads of nodules (marked by the red arrows), varying in size, emerged within the pulmonary expanse, with a conspicuous prominence residing within the mid-lobe of the dexter lung, proximate to the hilus. The cross-sectional dimensions of this remarkable entity measured approximately 3.7 x 4.1cm. (C, D) An assortment of inconstant masses (marked by the red arrows) materialized alongside the right abdominal wall and the formidable psoas major muscle.
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case_images: CT and MRI imaging ( Figure 3 ) revealed abdominal recurrence and additional metastasis to both lungs.
case_images: Showcases the compelling pathological discoveries derived from the percutaneous biopsy of the enigmatic pelvic wall mass. A positive expression of PAX8, but negative expression for the thyroid-specific markers thyroglobulin (TG) and thyroid transcription factor-1(TTF-1), and the expression of Ki-67 proliferation index was low, about 5%, and the PD-L1 was negative.
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case_images: Additionally, PD-L1 (programmed death ligand-1) was found to be negative ( Table 1 ;  Figure 4 ).
case_images: Treatment outcome evaluated by imaging. Compared to the pre-radiotherapy and systemic treatment phase involving a combination of pazopanib and the PD-1 checkpoint inhibitor toripalimab, it is evident through the utilization of advanced imaging techniques such as CT scans and MRI studies that a significant reduction in tumor size (the area outlined by red line) and quantity (the green arrow indicates that the metastatic tumor is almost gone) has been achieved within the pulmonary and abdominal pelvic regions. After 8 months later, the lesions on the lung progressed due to irregular toriplimab treatment, but the lump in the abdomen was still shrinking.
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case_images: And two months later, the masses in the abdomen and lungs had both shrunk, as assessed by imaging studies ( Figure 5 ), after radiotherapy and 2 courses of the above systemic treatment strategies. Unfortunately, due to the patient's personal reasons, irregular toriplimab treatment was carried out about 3 months every time, and the lesions on the lung progressed, but the lump in the abdomen was still shrinking after 8 months ( Figure 5 ).