[Pathological characteristics of cytologically diagnosed metastatic clear cell renal cell carcinomas]

Objective: To investigate the clinical, cytopathological characteristics, and differential diagnosis of metastatic clear cell renal cell carcinomas (CCRCC). Methods: Nine cases of metastatic CCRCC cytologically diagnosed in the Department of Pathology, the First Affiliated Hospital of Air Force Medical University from July 2021 to December 2024 were collected. The HE staining, May-Grunewald-Giemsa staining, liquid-based slides, cell block preparation, and immunocytochemistry of EnVision two-step staining were performed. The clinical and cytopathological features, treatments and follow-up data were analyzed in combination with literature review. Results: Among the 9 cases of metastatic CCRCC, there were 7 males and 2 females. The age range was 43-78 years, and the average age was 63.6 (57.5, 72.5) years. The metastatic sites were lymph node in 3 cases (2 cases of mediastinal lymph nodes and 1 case of left cervical lymph node), bone in 3 cases (pubis, thoracic vertebrae and femur, respectively), thyroid in 2 cases, and adrenal gland, lung and pancreas in 1 case, respectively. Two of the 9 cases had two metastatic sites (case 8 had metastases of lung and mediastinal lymph nodes; case 9 had metastases of thyroid and cervical lymph nodes). The median time from the diagnosis to metastasis was 9.4 years (range 1.1 to 13.8 years). The tumor cells were arranged in papillary, acinar, sheet, cluster or single scattered pattern. Most cases had uniform nuclei with mild atypia and inconspicuous nucleoli, while some cases had variable nuclei with prominent nucleoli. The cytoplasm of the tumor cells was abundant. Some cases showed clear cytoplasm with small vacuoles, while some of them showed eosinophilic and granular cytoplasm. Immunocytochemically, the tumor cells were positive for CKpan(AE1/AE3,6/6), PAX8 (9/9), CAⅨ (9/9), CD10 (9/9), and vimiten (8/8). Patients were treated primarily with targeted therapy and/or immunotherapy and curettage and radiation therapy for bone lesions. The follow-up time ranged from 1.0 month to 41.5 months (median, 20 months), and all patients survived at the end of follow-up. Conclusions: The cytology of metastatic CCRCC often shows uniform cell size, abundant and clear cytoplasm, low nuclear/cytoplasmic ratio, and mild nuclear atypia. Its cytological diagnosis is challenging because it occurs in various sites and needs to be differentiated from primary tumors of these sites. Emphasis should be placed on the morphological recognition of CCRCC, and immunocytochemical staining should be used to improve diagnosis. When necessary, molecular testing can be employed for diagnosis. Meanwhile, the medical history should be carefully inquired by pathologists to avoid missed diagnosis and misdiagnosis.