Uterine smooth muscle tumors are the most common female genital tract neoplasms. While leiomyosarcoma has been studied at length, smooth muscle tumors of uncertain malignant potential (STUMPs) still have ambiguous and unresolved issues, with a risk of relapse and evolution largely undefined. We performed an array comparative genomic hybridization analysis on a primitive STUMP and its local recurrence, histologically diagnosed as undifferentiated sarcoma. To the best of our knowledge, our report is the first genomic study on primitive STUMPs and the different relapsed tumors. The results showed few copy number alterations shared between both samples and the high heterogeneity in the STUMP was apparently lost in the sarcoma. Surprisingly the STUMP presented an amplification of the BCL2 gene, not observed in the relapsed tumor. Additionally, fluorescence in situ hybridization and immunohistochemical staining were performed to confirm BCL2 amplification and expression in these samples and in two other cases of primitive STUMPs and their corresponding relapsed tumors. The presence of BCL2 in multiple copies and expression in the two primitive STUMPs and two relapsed tumors was confirmed. The marked amplification of the BCL2 gene present in the primitive STUMP and the multiple copies also observed in other cases, suggest its potential role as a marker of STUMP malignant potential and recurrence.