Solid cancer is defined as an abnormal mass of tissue that forms a distinct, localized lump or growth within the body. This mass develops when cells in a specific organ or tissue begin to grow and divide uncontrollably. Solid tumors account for approximately 90% of all adult human cancers. This physical structure differentiates these malignancies from other types of cancer.
Defining Solid Tumors
The difference between a solid tumor and a non-solid, or liquid, cancer lies in its physical manifestation. Solid tumors, such as those found in the breast, lung, or prostate, form a cohesive, palpable mass of cells within an organ or tissue. This mass often remains confined to its original location for a period, which is known as localized growth.
Liquid cancers, also called hematologic malignancies, include conditions like leukemia and multiple myeloma. These cancers do not form a distinct mass but instead involve cancerous cells circulating freely throughout the body. They are primarily found in the blood, bone marrow, or lymphatic system.
Primary Categories of Solid Cancer
Solid cancers are primarily classified based on the type of cell from which they originate. The two major classification groups are carcinomas and sarcomas, which reflect the tissue layer involved.
Carcinomas are the most frequent type of solid cancer, originating in epithelial cells that line the internal and external surfaces of the body. Epithelial tissue forms the covering of organs, the skin, and the lining of ducts and glands. Common examples include breast cancer, lung cancer, colon cancer, and prostate cancer, all of which arise from epithelial surfaces.
Sarcomas are less common and develop from mesenchymal cells, which constitute the body’s connective tissues. These include bone, muscle, fat, cartilage, and blood vessels. For instance, osteosarcoma begins in the bone, while liposarcoma originates in fat tissue.
Diagnostic Pathway and Staging
The diagnostic process moves from detection to confirmation and then to measuring the disease extent. Initial detection often involves imaging techniques, such as computed tomography (CT) scans, magnetic resonance imaging (MRI), or ultrasound, to visualize the mass and determine its size and location. This is followed by a biopsy, where a small tissue sample is removed and examined by a pathologist to confirm the presence of cancerous cells.
Confirmation of cancer leads to the process of staging, which determines the anatomical extent of the disease. The universally accepted method is the TNM system, which uses three factors to assign an overall stage. The “T” describes the size of the primary Tumor, the “N” indicates whether the cancer has spread to nearby lymph Nodes, and the “M” denotes the presence of distant Metastasis.
Staging is distinct from grading, although both are necessary to guide treatment decisions. Staging indicates how far the cancer has spread within the body, while grading describes the appearance and predicted aggressiveness of the cancer cells themselves. Pathologists assign a grade by examining the cells under a microscope to see how closely they resemble normal, healthy cells. Low-grade tumors are considered well-differentiated and generally slower-growing, whereas high-grade tumors are poorly-differentiated and are expected to grow and spread more rapidly.
Core Treatment Approaches
Treatment for solid cancer is often multimodal, meaning it involves a combination of local and systemic therapies tailored to the specific type and stage of the tumor. Because solid tumors are physically localized, surgery remains a primary option, especially when the cancer is detected in an early stage. The procedure involves removing the entire tumor mass along with a margin of surrounding healthy tissue to reduce the likelihood of recurrence.
Radiation therapy is another local treatment that uses high-energy beams to destroy cancer cells in a targeted area while minimizing damage to adjacent healthy structures. It can be used before surgery to shrink a large tumor, after surgery to eliminate residual cells, or as the main treatment when surgery is not feasible. These local approaches are often combined with systemic treatments, which are designed to travel throughout the body to kill cancer cells that may have spread beyond the initial site.
Systemic treatments include traditional chemotherapy, which kills rapidly dividing cells, and more modern targeted therapy. Targeted drugs work by blocking specific molecular pathways or proteins, or biomarkers, that are involved in the growth and survival of cancer cells. These agents can interfere with cell growth signals, block the formation of new blood vessels that feed the tumor, or carry toxins directly to the cancer cell.
Immunotherapy has emerged as a major systemic pillar, harnessing the body’s own immune system to fight the cancer. Immune checkpoint inhibitors are a type of immunotherapy that block proteins like PD-1 or CTLA-4, which cancer cells use to switch off the immune system’s T-cells. By “releasing the brakes” on the T-cells, these drugs enable the immune system to recognize and mount an effective attack against the solid tumor.