The TNM classification for thymic tumors calculator assesses the stage of thymic tumors based on the user's input regarding tumor classification, lymph node classification, and metastasis classification. The staging process uses predefined categories within each input to determine the appropriate stage of the tumor, ranging from Stage I to Stage IVB. If the inputs do not conform to any of the specified categories, the stage cannot be fully assessed.

Inputs:

Tumor classification:
- Tx: Primary tumor cannot be assessed
- T0: No evidence of primary tumor
- T1a: Tumor encapsulated or extending into the mediastinal fat with no mediastinal pleura involvement
- T1b: Tumor encapsulated or extending into the mediastinal fat with direct invasion of mediastinal pleura
- T2: Tumor with direct invasion of the pericardium (either partial or full thickness)
- T3: Tumor with direct invasion into lung, brachiocephalic vein, superior vena cava, phrenic nerve, chest wall, or extrapericardial pulmonary artery or veins
- T4: Tumor with invasion into aorta (ascending, arch, or descending), arch vessels, intrapericardial pulmonary artery, myocardium, trachea, or esophagus

Lymph node classification:
- Nx: Regional lymph nodes cannot be assessed
- N0: No regional lymph node metastasis
- N1: Metastasis in anterior (perithymic) lymph nodes
- N2: Metastasis in deep intrathoracic or cervical lymph nodes

Metastasis classification:
- M0: No pleural, pericardial, or distant metastasis
- M1a: Pleural or pericardial metastasis
- M1b: Pulmonary intraparenchymal or distant organ metastasis

Computation:

The possible stages are determined through a series of conditional checks on the inputs, leading to the following outcomes:

Stage I: Tumors classified as T1a or T1b with no regional lymph node metastasis (N0) and no pleural, pericardial, or distant metastasis (M0).

Stage II: Tumors classified as T2 with no regional lymph node metastasis (N0) and no pleural, pericardial, or distant metastasis (M0).

Stage IIIA: Tumors classified as T3 with no regional lymph node metastasis (N0) and no pleural, pericardial, or distant metastasis (M0).

Stage IIIB: Tumors classified as T4 with no regional lymph node metastasis (N0) and no pleural, pericardial, or distant metastasis (M0).

Stage IVA: Tumors classified as T1a, T1b, T2, T3, or T4 with metastasis in anterior lymph nodes (N1) and no distant metastasis (M0), or with pleural or pericardial metastasis (M1a) regardless of lymph node classification.

Stage IVB: Tumors with deep lymph node involvement (N2) or distant metastasis (M1b), with any tumor (T) classification.

If the inputs do not match any defined combination, the output is "Stage cannot be fully assessed."

Output:

The final result is returned as a string indicating the tumor stage, based on the user's input. If any input is missing or invalid, the output prompts users to provide selections for all inputs.

The TNM classification for thymic tumors is a clinical staging system developed by the American Joint Committee on Cancer (AJCC). It is designed for the purpose of categorizing thymic tumors based on the extent of the disease, which is crucial for determining the appropriate treatment strategy and predicting patient prognosis.

The primary components of this classification system are the tumor size and extent (T), the involvement of regional lymph nodes (N), and the presence of distant metastasis (M). Each of these components is assigned a numerical value based on the severity or extent of the disease. The T component ranges from T1 (small, localized tumors) to T4 (tumors that have invaded into surrounding structures). The N component is either N0 (no regional lymph node involvement) or N1 (regional lymph node involvement), and the M component is either M0 (no distant metastasis) or M1 (distant metastasis).

The final TNM stage is determined by combining the T, N, and M components. This stage can range from stage I (early disease) to stage IV (advanced disease), with each stage further subdivided based on the specific T, N, and M values. This comprehensive classification allows for a standardized comparison of patient outcomes and the effectiveness of different treatment modalities.