Background: Aggressive angiomyxoma is a rare entity within mesenchymal cell neoplasms, especially in pregnant women. Its main characteristic is the ability to infiltrate neighboring structures and to recur. Case Presentation: We present the case of a pregnant woman who debuted with a genital prolapse in the second trimester of pregnancy. She was diagnosed with bilateral ovarian teratomas and a pelvic mass of which the diagnosis could not be established until delivery. The route of delivery used was cesarean section since the genital prolapse behaved as a previous tumor. After the puerperium, the patient was referred for consultation to complete the study of the mass. The extension study was carried out with a negative result. The patient underwent surgery for tumor exeresis. Hormonal treatment was not administered according to the patient’s preferences. Conclusions: Aggressive angiomyxoma is a benign neoplasm that should be considered in the differential diagnosis of pelvic tumors in women. In pregnant women, the vaginal route of delivery is not contraindicated as long as the tumor does not obstruct the birth canal. The definitive treatment is surgery, preferably performed in a second stage after delivery.

Uterine adenosarcoma with sarcomatous overgrowth (ASSO) is an exceptionally rare and aggressive subtype of uterine sarcomas, characterized by high mitotic activity, deep myometrial invasion, and an elevated risk of recurrence and metastasis. We report the case of a 79-year-old institutionalized woman with a history of hypertension, type 2 diabetes, chronic hepatitis B, and mild Alzheimer’s disease. During routine hepatic ultrasound surveillance, an incidental 26 mm endometrial lesion was detected. Initial diagnostic hysteroscopy revealed a benign endometrial polyp. However, due to the patient’s institutionalization and absence of gynecologic symptoms, no specialized follow-up was conducted. Four years later, she presented with profuse postmenopausal bleeding. Imaging revealed a markedly enlarged uterus with a 12–13 cm heterogeneous endometrial mass containing cystic and hemorrhagic areas, demonstrating diffusion restriction and significant contrast enhancement on MRI, with no radiologically suspicious lymphadenopathy. Hysteroscopy demonstrated a giant polyp with a broad implantation base; histology suggested sarcomatous transformation. Definitive diagnosis after total hysterectomy with bilateral salpingo-oophorectomy confirmed high-grade ASSO with homologous sarcomatoid overgrowth, consistent with endometrial stromal sarcoma. This case illustrates the progressive malignant transformation of an initially benign-appearing lesion in a patient with significant comorbidities and limited follow-up. It underscores the importance of clinical vigilance, regular monitoring, and interdisciplinary coordination in the evaluation of uterine enlargement in asymptomatic postmenopausal women.