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The Value of Mitotic Count and Ki67 Proliferation Index in Congenital Mesoblastic Nephroma

ABSTRACT Objective: We aimed to define the histopathologic features and proliferative rate of congenital mesoblastic nephroma (CMN) as a risk factor for recurrence. Methods: Fourteen cases of CMN among 138 registered pediatric renal tumors were retrospectively reviewed. The prognostic impact for mitotic rate and Ki67 index was investigated. Results: There were four (28.6%) classic, six (42.9%) cellular, and four (28.6%) mixed type CMNs, with average Ki-67 counts of 16.75% in the classic CMN, and 53.2% in the tumors with cellular components (both mixed and cellular CMNs). Twelve patients (85.7%) were aged less than six months. Tumors with cellular component showed significantly larger tumor diameter and higher Ki-67 index (p = 0.015 and p = 0.016, respectively). The patient with cellular CMN, whose tumor showed the highest mitotic rate (4.9/HPF), but not the highest Ki67 index (57.4%), died of recurrent disease with distant metastasis. Conclusion: Proliferative markers-mitotic count and Ki67 index-have limited value to predict recurrence or metastasis in CMNs with a cellular component.