A patient with partial malignant transformation of endometriotic cysts had a clear history of endometriosis and bilateral ovarian coarctation and underwent bilateral ovarian cyst removal, but was not followed up regularly after surgery and had no awareness of health check-ups. Later, due to the symptoms of pelvic pain, she was found to have cysts in both ovaries at the local clinic, of which the right mass was multifocal and had abundant blood flow on the separation. I don’t know what the reason was for not having surgery and not following up closely, but two years later when I reviewed the patient again, I found that the mass was growing rapidly, especially the right mass, and multiple papilla-like strong echogenicity appeared on the separation, and solid occupancy was visible in the wall of the capsule, accompanied by abnormal increase of serum CA-125, so the preoperative diagnosis of malignant change of the coarctation was basically clear at this time. After transferring to the hospital, because the doctor was alert to the malignant change, the patient was fully prepared for the intestine before surgery, operated carefully and cautiously, complete resection of the right adnexa was performed, the specimen was carefully dissected under the table, and solid rotten tissue growth was found in the cyst, and a rapid frozen pathological examination was applied for the suspicious area in time, so that a very formal and comprehensive exploration and staging surgery was performed for the patient according to the standard of ovarian malignant tumor The patient underwent a very formal and comprehensive exploration and staging surgery according to the standard of ovarian malignancy. Surgical pathological staging: stage Ia highly differentiated endometrioid carcinoma of the right ovary. She was not treated with chemotherapy after surgery and was followed up without recurrence. It is now more than 2 years postoperatively and the prognosis is good. Lessons learned: Although endometriosis is a benign disease, it has the possibility of recurrence and malignancy. A long-term follow-up plan should be formulated for the patient after surgery, and the importance of regular gynecologic examinations should be repeatedly emphasized. Imaging is an important tool to detect malignant changes. Ultrasound examination is noninvasive and easily accepted, and if the diagnosis is not clear, further MRI can be requested. The presence of contrast-enhanced nodules on the cyst wall of the coarctation cyst is the most important clue for the diagnosis of malignant changes in the endometriosis cyst. If the doctor had paid enough attention to the malignant change of endoheterocyst when the patient was first found to have recurrence of the cyst two years ago, further serum CA-125 test or further MRI examination could have been requested to obtain more favorable evidence and the patient could have received surgery as early as possible. In recent years, the incidence of endoheterosis has been increasing and has become a common gynecological condition, and the problem of its malignant transformation needs to be paid high attention. As early as 1925, Sampson first reported the malignant transformation of endoheterosis. The following three criteria were used to confirm the diagnosis: (1) the presence of both endometriosis and carcinoma in the same ovarian tissue, but not all patients have this typical presentation; (2) similar histological relationship between endometriosis and carcinoma; (3) the need to exclude metastatic tumors. The incidence of malignant transformation has been reported in the literature to be in the range of 0.7%-1.0%, which is probably a conservative figure and may be higher in reality. Malignant transformation is mainly concentrated in the ovary, endometrioid carcinoma and clear cell carcinoma are the two most common pathological types of coeliac malignancy, but cases of malignant transformation in other sites, such as the intestine, vaginal-rectal compartment, etc., are constantly being identified and reported. The pathogenesis of malignant changes in endometriosis is still unclear, as it was thought that estrogen may play an important role, but now it is thought that it may be related to metabolic and genetic factors. Once diagnosed, women of childbearing age should be closely monitored and followed to prevent malignant changes. Preoperative diagnosis may sometimes be difficult, and patients should be noted for changes in clinical symptoms and timely requests for imaging (ultrasound and MRI) and serum tumor markers. In a recent multicenter retrospective study published in January 2010, LimMC from Korea reported that in 221 patients with epithelial carcinoma combined with ovarian endometriosis, the most common clinical symptom was pelvic pain, followed by gastrointestinal symptoms, palpable masses, abdominal distention, vaginal bleeding, new or worsening dysmenorrhea and painful intercourse. The age of onset of ovarian malignancies associated with endometriosis tends to be 10-20 years younger than in patients without comorbid endometriosis, and early detection and treatment are again the most effective means of improving prognosis. In addition, large epidemiologic studies have found that patients with endometriosis are at increased risk of developing extra-ovarian malignancies, such as breast cancer and non-Hodgkin’s lymphoma, requiring increased vigilance by clinicians.