Even though there are several cancer staging systems, the American Joint committee on Cancer (AJCC) TNM staging system is the most used by clinical oncologists worldwide and is the standard in cancer staging. During the 20th century, the Union for the International Control of Cancer, created a clinical system for cancer staging, known as TNM, based on the local tumor extension (T), lymph node invasion (N), and presence or absence of metastasis (M) distant from the local origin. The TNM system allowed clinicians to use similar treatments on cancer patients around the world and has proven to be the most successful guide in clinical oncology. The TNM staging system has been modified regularly by the AJCC over the past years, to improve uniform clinical practices in cancer treatments; multidisciplinary teamwork including managing physician, pathologist, and radiologist, created the basis for clinical trials and for evaluating outcomes. The oncologist treating physician is responsible for assigning the TNM stage of patients. The current TNM staging system in the 2018 recent publication is better than its original form because it has incorporated new information that improved treatment results; however, discrepancies still exist, for example, biomarkers as estrogen receptor, progesterone receptor, and human epidermal growth factor receptor that have shown to be important prognostic factors have not been included in the actual TNM staging system for breast cancer.