Stomach cancer, medically known as gastric cancer, is a disease where malignant cells form in the lining of the stomach. Staging is a standardized system doctors use to describe the size of the tumor and whether it has spread from its original location. This classification is essential for determining the appropriate treatment plan and predicting the patient’s outlook. The staging system for stomach cancer divides the disease into five primary categories, designated as Stage 0 through Stage IV.
Understanding the Staging Framework
The extent of stomach cancer is categorized using the American Joint Committee on Cancer (AJCC) TNM system. This framework uses anatomical and biological criteria to describe the cancer’s progression. The letters T, N, and M represent the factors that determine the overall numerical stage.
The “T” component describes the size and extent of the primary tumor, specifically how deeply it has grown into the layers of the stomach wall. The stomach wall consists of five layers, and the depth of penetration is a major factor in determining the T classification. The “N” component indicates whether the cancer has spread to nearby lymph nodes and, if so, how many are involved.
The “M” factor indicates whether metastasis has occurred, meaning the cancer has spread to distant organs or tissues away from the stomach. This factor signifies advanced disease. By combining the specific T, N, and M designations, doctors assign the cancer a single numerical stage, ranging from 0 to IV.
Defining the Five Stages
The five stages classify the disease based on the combined T, N, and M factors. Stage 0, known as carcinoma in situ, is the earliest form of the disease. Cancerous cells are found only in the innermost lining (mucosa) of the stomach and have not grown into deeper tissue layers.
Stage I represents minimal invasion and is divided into substages (IA and IB). In Stage IA, the tumor has grown into the mucosa or submucosa but has not spread to any lymph nodes. Stage IB involves growth into the muscle layer without lymph node involvement, or spread to one or two nearby lymph nodes while remaining in the inner layers.
Stage II indicates deeper penetration into the stomach wall or a greater number of affected lymph nodes. The cancer may have reached the submucosa and spread to up to six nearby lymph nodes. Alternatively, it might have grown through the thick muscle layer (muscularis propria) and spread to a smaller number of lymph nodes. Stage II cancers have not yet spread to distant sites.
Stage III signifies extensive local or regional spread, often involving growth through the full thickness of the stomach wall or spread to a significant number of lymph nodes. This stage is sub-divided (IIIA, IIIB, IIIC) because the combination of tumor depth and lymph node involvement varies widely. For example, Stage III could involve spread to the outer layer (serosa) or growth into nearby organs, combined with spread to multiple lymph nodes.
Stage IV is the most advanced stage, indicating the disease has metastasized. This means the cancer has spread to distant parts of the body, such as the liver, lungs, or non-regional lymph nodes. Stage IV is defined solely by the presence of distant spread, regardless of the size of the primary tumor or local lymph node involvement.
How Doctors Determine the Stage
Assigning a specific stage requires diagnostic procedures to gather the necessary T, N, and M data. The process begins with an upper endoscopy, which uses a flexible tube and camera to visualize the stomach lining and obtain a biopsy. The biopsy is the only way to confirm the presence of cancer cells.
To determine the depth of the tumor (T factor) and local lymph node involvement (N factor), an endoscopic ultrasound (EUS) is often performed. The EUS uses an ultrasound probe to create detailed images of the stomach wall layers and surrounding lymph nodes. This procedure assesses how far the cancer has penetrated the stomach.
Imaging tests check for distant spread (M factor). Computed tomography (CT) scans of the chest, abdomen, and pelvis are routinely used to look for cancer spread to organs like the liver or lungs. Positron emission tomography (PET) scans may also be used to identify areas of increased metabolic activity characteristic of cancer cells. Sometimes, doctors perform exploratory surgery, such as laparoscopy, to visually inspect the abdominal cavity and obtain samples for accurate staging before definitive treatment.
General Treatment Paths by Stage
The cancer stage is the primary factor guiding treatment choice. For the earliest stages (Stage 0 and Stage I), treatment focuses on removing the cancer entirely. This usually involves surgery (gastrectomy) to remove part or all of the stomach, along with nearby lymph nodes. For very small, early-stage tumors, an endoscopic resection may be used to remove the cancer without major surgery.
For intermediate cancers (Stage II and Stage III), a multimodal approach is employed. The goal is complete surgical removal, but the risk of recurrence is higher due to deeper spread. Treatment often involves chemotherapy or chemoradiation given before surgery (neoadjuvant therapy) to shrink the tumor, followed by gastrectomy. Chemotherapy or chemoradiation may also be given after surgery (adjuvant therapy) to eliminate remaining cancer cells.
In Stage IV, the cancer has spread to distant organs, and the disease is considered systemic. Surgery to remove the primary tumor is usually not curative, so the focus shifts to systemic therapies. These treatments include chemotherapy, targeted therapy drugs that attack specific molecular features of the cancer, and immunotherapy. Palliative care is also a component at this stage, focusing on controlling symptoms and improving the patient’s quality of life.