Unconventional Histopathological Features With <i>KIAA1549::BRAF</i> Fusion in Advanced Prostatic Adenocarcinoma

This report delineates an intriguing example of advanced prostatic adenocarcinoma displaying distinctive histopathological characteristics associated with a <i>KIAA1549::BRAF</i> fusion, a genomic anomaly predominantly identified in central nervous system tumors. A 66-year-old man, presenting with acute renal failure, exhibited metastatic disease involving pelvic soft tissue, bladder, liver, and bone. Histological examination revealed a markedly unconventional morphology within the prostate, characterized by infiltrative tumor sheets exhibiting abundant vacuolated cytoplasm, hyperchromatic nuclei, and irregular nuclear membranes, distinct from typical prostatic adenocarcinoma. Immunophenotyping confirmed NKX3.1 positivity and GATA3 negativity. Molecular analysis revealed the rare <i>KIAA1549::BRAF</i> fusion alongside pertinent mutations in phosphatidylinositol 3-kinase, phosphatase and tensin homolog, and tumor protein 53 genes. Despite diverse therapeutic interventions targeting mitogen-activated protein kinase signaling and subsequent clinical trial enrollment, disease progression remained relentless, culminating in the patient's demise within 4 years of diagnosis. This report highlights the exceptional histopathological presentation associated with <i>KIAA1549::BRAF</i> fusion in prostatic adenocarcinoma, emphasizing the need for a deeper comprehension of its implications on disease behavior and therapeutic responsiveness in similar instances.