[Nested variant of urothelial carcinoma complicated with pulmonary lymphangitis carcinomatosis. Case report].

Background: Nested variant of urothelial carcinoma is a rare entity characterized by a particularly aggressive clinical course and a poor prognosis. Although disease progression can involve the lung parenchyma, pulmonary carcinomatous lymphangitis is an exceptionally rare manifestation. Up until the date of this publication, evidence in literature is limited, highlighting the rarity of this pattern of dissemination and the importance of its timely recognition. Clinical case: A 72-year-old man with initial macroscopic hematuria, who was diagnosed with nested variant of urothelial carcinoma with infiltration of the lamina propria. Despite transurethral resection of the tumor and subsequent systemic treatment with platinum-based chemotherapy, the patient experienced rapid disease progression, which was characterized by pelvic and mediastinal lymph node infiltration, pulmonary lymphangitic dissemination, bilateral hydronephrosis, and thrombosis of the right internal jugular vein, as well as the left common iliac, external iliac, and femoral veins. Conclusions: This report documents a case of muscle invader nested variant of urothelial carcinoma, whose evolution was complicated by pulmonary carcinomatous lymphangitis, an extremely rare manifestation. Early recognition of this variant is essential to guide the diagnostic and therapeutic approach in patients with high-risk histological variants.