This bidirectional cohort study (retrospective + prospective) focuses on three key challenges in oral mucosal melanoma (OMM): clinical staging based on depth of invasion (DOI), molecular subtyping, and precision therapy. By integrating DOI-driven T-stage reclassification, genomic profiling, and longitudinal follow-up, we aim to build a population-specific, high-quality evidence resource to support refined staging, CDK4-targeted treatment, and prognostic modeling for Chinese OMM patients.

Study Design This is a multicenter, bidirectional (retrospective + prospective) observational cohort study designed to establish a high-quality evidence platform for oral mucosal melanoma (OMM), a rare malignancy with high aggressiveness and poor prognosis. The study is conducted at four tertiary hospitals in China: Shanghai Ninth People's Hospital (lead center), Air Force Medical University Stomatological Hospital, Xiangya Hospital of Central South University, and Sun Yat-sen Memorial Hospital of Sun Yat-sen University.

Study Population The cohort will include a total of 1,100 Chinese patients with histopathologically confirmed primary OMM.

Retrospective cohort (n=800): Patients diagnosed between January 2015 and June 2025, with complete medical records, pathological slides, and available follow-up data.

Prospective cohort (n=300): Consecutive newly diagnosed patients enrolled from July 2025 to December 2028, after providing written informed consent.

Inclusion Criteria:

• Histopathologically confirmed primary oral mucosal melanoma (WHO criteria);

Primary site: oral mucosa (palate, gingiva, sublingual, buccal, hard palate, floor of mouth);

Receiving or planning standard treatment (surgery, radiotherapy, chemotherapy, immunotherapy, or targeted therapy);

Age ≥18 years, any sex;

Complete clinical data with pathology, imaging, and records (retrospective) OR willingness for long-term follow-up (prospective);

Signed informed consent (prospective) or data meeting ethical waiver (retrospective).

Exclusion Criteria:

• Primary melanoma originating from skin, eye, esophagus, or other non-oral mucosal sites;

Secondary/metastatic oral mucosal melanoma (primary not in oral cavity);

Unavailable key clinical information (surgical records, pathology, imaging);

Prior or concurrent other malignancy interfering with prognosis;

Severe mental/cognitive disorders or poor compliance;

Severe comorbidities (heart failure, liver/renal failure) affecting treatment or survival analysis;

Patient refusal or withdrawal of informed consent.

Histopathologically confirmed primary oral mucosal melanoma