MKI67 and mesenchymal cell neoplasm: While angiomyofibroblastoma (AMFB) is uniformly benign in biological behavior, as evidenced by the low Ki-67 proliferation index (10%) in our case and excellent post-resection outcomes reported in literature, its histological overlap with more aggressive mesenchymal tumors like aggressive angiomyxoma creates persistent diagnostic challenges, particularly in unusual anatomical locations such as the retroperitoneum.