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The TNM classification system is used to stage bone cancer specific to the appendicular skeleton, trunk, skull, and facial bones. To determine the stage, the system evaluates four critical inputs:

- Tumor Classification:
  - Tx: Primary tumor cannot be assessed
  - T0: No evidence of primary tumor
  - T1: Tumor <= 8 cm in greatest dimension
  - T2: Tumor > 8 cm in greatest dimension
  - T3: Discontinuous tumors in the primary bone site

- Lymph Node Classification:
  - Nx: Regional lymph nodes cannot be assessed
  - N0: No regional lymph node metastasis
  - N1: Regional lymph nodes metastases present

- Distant Metastasis:
  - M0: No distant metastasis
  - M1a: Metastasis confined to lung
  - M1b: Metastases in bones or other distant sites

- Histologic Grade:
  - Gx: Grade cannot be assessed
  - G1: Well differentiated
  - G2: Moderately differentiated
  - G3: Poorly differentiated
  - G4: Undifferentiated

Using these inputs, the system computes the cancer stage, which aids in determining prognosis and treatment. Here's how the classification maps to different stages:

- Stage IA is indicated by a tumor that is 8 cm or less (T1), with no lymph node involvement (N0), no distant metastasis (M0), and a histologic grade of G1 or G2.
- Stage IB involves a larger tumor (greater than 8 cm, T2), still with no lymph node spread (N0), no distant metastasis (M0), and the tumor is graded as well or moderately differentiated (G1 or G2).
- Stage IIA is characterized similarly to Stage IA but with a worse histologic grade (G3 or G4).
- Stage IIB encompasses a larger tumor (T2) with no lymph node spread (N0) and no distant metastasis (M0), but with a more aggressive histologic grade (G3 or G4).
- Stage III is applied to discontinuous tumors in the bone site (T3) that have not metastasized to the lymph nodes (N0) or beyond (M0), regardless of the histologic grade.
- Stage IVA includes any primary tumor size (T1, T2, T3) with no lymph node metastasis (N0) but with metastasis confined to the lung or other less extensive sites (M1a or M1b).
- Stage IVB involves scenarios where there is regional lymph node metastasis (N1) and can include various combinations of tumor size and distant metastasis presence, including more aggressive distant spread (M1b) across any histologic grade.

The system methodically combines these classifications to offer a stage outcome, which is crucial for clinical decisions and patient management.

The calculator in question is the TNM Classification for Bone Cancer, specifically for the appendicular skeleton, trunk, skull, and facial bones. TNM stands for Tumor, Node, Metastasis. This classification system is used by clinicians to stage different types of cancer, including bone cancer, based on the size and extent of the tumor (T), the involvement of lymph nodes (N), and the presence of distant metastasis (M).

This calculator is applicable to patients who have been diagnosed with bone cancer. It helps in determining the stage of the cancer, which is crucial for planning the appropriate treatment strategy and predicting the patient's prognosis. 

The TNM classification does not have specific exclusion criteria. However, it may not be applicable or accurate in cases where the cancer has spread to multiple distant sites, or in patients with certain rare types of bone cancer. It is also less useful in pediatric patients, as bone cancer in children often behaves differently than in adults.

TNM classification for bone cancer (appendicular skeleton, trunk, skull, and facial bones)

Giant cell tumor of bone

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