Phyllodes tumor (PT) is a rare type of breast tumor made up of both connective tissue (stroma) and gland tissue (epithelium). It accounts for less than 1% of all breast tumors. The main symptom is a fast-growing, painless lump.

Based on its appearance under a microscope, the World Health Organization (WHO) classifies PT into three grades: benign (non-cancerous), borderline (intermediate), and malignant (cancerous). The chance of the tumor coming back after treatment (recurrence) is about 7%, 17%, and 25% for each grade, respectively. The average age when patients are diagnosed is between 36 and 55 years, and the typical tumor size ranges from about 4 to 11 cm. Malignant PT can spread to other parts of the body (metastasis) in up to 6% to 62% of cases, most often to the lungs or bones through the bloodstream.

Because PT is rare, large studies on its causes, diagnosis, treatment, and long-term outlook are very limited. PT can grow very quickly. Delaying diagnosis and treatment may allow the tumor to become so large that surgery is no longer an option. Standard imaging tests (ultrasound, mammogram, MRI) have limited ability to tell the difference between benign and malignant PT. Also, since these tumors are often large and vary from one area to another, a small needle biopsy may not show the whole picture. An accurate grade is usually only possible after the whole tumor is removed and examined by a pathologist.

PT does not respond well to radiation or chemotherapy. Therefore, the main treatment is complete surgical removal with clear margins. The role of newer therapies such as targeted therapy or immunotherapy is still being studied. Although the WHO grade gives some idea of how the patient might do, some benign PT can come back many times or even turn malignant, while some malignant PT stay stable for a long time. The current grading system does not fully explain why individual outcomes differ.

In recent years, most prediction models for PT have been built using Western patient data (for example, from the SEER database). These models have not been tested in Asian populations. They are usually based on small, single-center studies with dozens to a few hundred patients, and many have only been checked inside the same database without outside (external) validation. Most studies focus on symptoms, imaging findings, how to tell benign from malignant PT, or comparing different types of surgery. Few have looked closely at patterns of recurrence and metastasis, or risk factors for rare events like multiple recurrences, distant spread, or death.

To fill these gaps, we plan to conduct a large, multi-center, retrospective (looking back at past medical records) study across 8 top hospitals in China. We will use real-world data from about 3,500 patients with breast PT diagnosed between 2001 and 2023. The main goals are to describe the clinical and pathological features, treatment patterns, and long-term outcomes of Chinese PT patients. The main outcomes we will measure are local recurrence, distant metastasis, and overall survival. Secondary outcomes include disease characteristics and current treatment practices. This study aims to provide evidence from the Chinese population to help guide personalized treatment and future updates to clinical guidelines.

Inclusion Criteria:

• Breast phyllodes tumors (benign, borderline, or malignant) based on postoperative paraffin pathology according to WHO criteria
• Underwent surgical treatment
• Complete or substantially complete clinical records, pathology reports, and follow-up data

Exclusion Criteria:

• Phyllodes without histological grading
• Hstory of other concomitant diseases that may affect the assessment of the study endpoint events
• Patients lost to follow-up or with missing key data

This study includes patients who underwent surgical resection for breast phyllodes tumor (PT) at one of eight tertiary hospitals in China between January 1, 2001, and December 31, 2023. All patients with a postoperative paraffin-embedded pathology diagnosis of benign, borderline, or malignant PT according to WHO criteria are included. Exclusion criteria are: (1) PT with uncertain behavior or unclassified grade; (2) history of prior malignancy (excluding breast cancer) with less than 5 years disease-free survival, or concurrent diseases that may affect endpoint assessment; (3) loss to follow-up or missing critical data (pathological grade, surgical procedure, or follow-outcome). A total of approximately 3,500 eligible patients from eight participating centers will be enrolled. All patients are of Chinese ethnicity.