The goal of this clinical trial is to learn if intrauterine injection of "Recombinant Humanized Type III Collagen Lyophilized Fibers" works to treat endometrial cancer or atypical hyperplasia in patients seeking fertility-preserving treatment. It will also learn about the safety of this intervention.The main questions it aims to answer are:

1. Does the combination of recombinant humanized type III collagen and progestin significantly increase the tumor remission rate at 6 months compared to progestin alone?
2. What medical problems do participants have when receiving this treatment (e.g., allergic reactions, abnormal inflammatory markers, or histocompatibility issues)? Researchers will compare "recombinant humanized type III collagen plus progestin (experimental group)" to "high-dose progestin alone (control group)" to see if the combination therapy is more effective for fertility preservation.

Participants will:

1. Take high-dose progestin (such as Medroxyprogesterone Acetate or Megestrol Acetate) orally every day.
2. If assigned to the experimental group, receive one intrauterine submucosal injection of collagen via hysteroscopy at months 0, 1, and 2, for a total of 3 injections.
3. Visit the clinic once every 3 months for treatment evaluation and follow-up, which includes hysteroscopic endometrial biopsy, imaging (such as transvaginal ultrasound), and safety tests for relevant biochemical indicators.

Inclusion Criteria:

1. Pathological diagnosis of endometrioid adenocarcinoma (G1 or G2) or atypical endometrial hyperplasia.
2. For patients with endometrial cancer, magnetic resonance imaging (MRI) or ultrasound must confirm that the lesion is confined to the endometrium or invades less than 1/2 of the myometrium (i.e., FIGO 2009 Stage IA).
3. Age ≤ 45 years.
4. Desire to preserve fertility and signed informed consent.
5. No serious medical comorbidities (e.g., severe liver or renal dysfunction).
6. No contraindications to progestin therapy or pregnancy.
7. No evidence of distant metastasis on imaging.

Exclusion Criteria:

1. Tumor invasion > 1/2 of the myometrium, or FIGO (2009) Stage IB and above.
2. Tumor differentiation grade G3 or non-endometrioid adenocarcinoma.
3. Coexistence of other malignant tumors.
4. Contraindications to conservative treatment or use of the study drugs.
5. Known allergy to recombinant protein components.
6. Acute genital tract inflammation or untreated abnormal vaginal discharge within 2 weeks prior to enrollment.
7. Previous treatment with high-potency progestin for more than 1 month.

General clinical data and fertility-sparing treatment outcomes of patients in both the experimental and control groups will be shared.

The data will be available within 6 months after the publication of the primary research paper.

Researchers interested in obtaining the clinical and treatment data can apply by contacting the principal investigator.