Stomach cancer, also referred to as gastric cancer, begins when cells in the stomach start to grow uncontrollably, often starting in the innermost layer of the stomach wall, the mucosa. This disease typically develops slowly over many years, with precancerous changes occurring before true cancer forms. Medical professionals use a standardized process called staging to determine the extent of the cancer within the body. Staging helps to classify how large the primary tumor is and whether it has spread to surrounding tissues or distant organs. The classification system provides a common language for doctors, which is important for predicting the likely outcome and planning the most appropriate treatment strategy.
How Doctors Determine the Stage
The standard method used to classify the extent of stomach cancer is the tumor, node, metastasis (TNM) system. This system evaluates three distinct components of the disease to assign a stage grouping, which ranges from 0 to IV, derived from combining the T, N, and M values.
The “T” component describes the extent of the primary tumor within the stomach wall. Scores range from T1 to T4, indicating how deep the cancer has grown into these layers. For example, T1 means the tumor has invaded only the inner layers, like the mucosa or submucosa. T4 means the tumor has grown through the stomach wall and potentially into nearby organs.
The “N” component assesses whether the cancer has spread to the regional lymph nodes near the stomach. This is quantified based on the number of lymph nodes found to contain cancer cells. N0 means no regional lymph node involvement. A higher N score, such as N3, indicates metastases in seven or more regional lymph nodes.
The “M” component determines if the cancer has metastasized to distant sites in the body, such as the liver or lungs. This component is categorized as M0, indicating no distant spread, or M1, confirming distant metastasis. Determining these values involves a combination of imaging tests, biopsies, and sometimes surgical exploration.
Understanding the Five Stages of Gastric Cancer
The staging process results in a classification that starts at Stage 0 and continues through Stage IV, with lower numbers representing less spread of the disease.
Stage 0, known as carcinoma in situ, describes cancer cells that are confined entirely to the innermost lining of the stomach, the mucosa. The cells have not grown into the deeper tissue layers and have not spread to any lymph nodes or distant organs. This highly localized stage is associated with the best potential outcomes.
Stage I signifies that the cancer has grown deeper into the stomach wall but remains relatively localized. Stage IA means the tumor has invaded the submucosa but has not spread to any lymph nodes. Stage IB can mean the cancer has grown into the muscle layer or has invaded the submucosa and spread to one or two nearby lymph nodes.
Stage II indicates that the cancer has either grown deeper into the stomach wall or has involved more nearby lymph nodes, or a combination of both. For instance, the cancer may have grown into the subserosa layer with limited lymph node involvement. It may also be less deep but have spread to three to six regional lymph nodes. The disease has still not spread to distant parts of the body.
Stage III represents advanced local or regional disease, involving extensive spread within the stomach or significant lymph node involvement. This stage includes scenarios where the tumor has grown through the stomach wall and into adjacent structures. It also includes cases when the tumor has seven or more positive regional lymph nodes. The defining factor of Stage III is the absence of distant metastasis.
Stage IV is the most advanced classification, signifying that the cancer has metastasized to distant organs or tissues. This spread beyond the regional lymph nodes is categorized by the M1 designation in the TNM system. Common sites for this distant spread include the liver, lungs, and the tissue lining the abdomen wall.
Treatment Strategies Based on Stage
The cancer stage plays a defining role in determining the overall treatment strategy and the expected outcome. Treatment approaches are fundamentally different depending on whether the disease is localized, regionally advanced, or metastatic.
For early-stage cancers, specifically Stages 0 and I, the primary goal is often curative, focusing on localized removal of the disease. Stage 0 tumors, confined to the inner lining, may sometimes be removed using minimally-invasive techniques like endoscopic resection. This involves removing the tumor through a tube-like instrument passed down the throat. Most Stage I cancers, however, require a gastrectomy, which is the surgical removal of part or all of the stomach, along with a lymph node dissection.
Treatment for Stages II and III typically employs a multi-modal approach due to the deeper invasion and extensive lymph node involvement. This strategy combines surgery, such as a gastrectomy and lymph node removal, with systemic treatments like chemotherapy and/or radiation therapy. These non-surgical treatments are often administered before surgery, known as neoadjuvant therapy, to shrink the tumor, or after surgery to eliminate any remaining cancer cells.
Once the disease has reached Stage IV, the focus of treatment shifts from attempting a cure to managing the disease and improving the patient’s quality of life. Since the cancer has spread widely, systemic treatments are prioritized to reach cancer cells throughout the body. These options include chemotherapy, targeted drug therapy, and immunotherapy. Surgery may still be performed in specific cases to manage complications, such as relieving a blockage or controlling bleeding, rather than for curative intent.