Cancer is a complex group of diseases characterized by the uncontrolled division and spread of abnormal cells within the body. These rogue cells ignore the normal signals that regulate cell growth and death, leading to an overabundance of tissue. To understand the various approaches to cancer diagnosis and treatment, it is helpful to categorize them based on their physical structure. The vast majority of diagnoses fall under the category known as solid cancers.
Defining Solid Cancer
A solid cancer is defined by the formation of an abnormal mass of tissue, commonly referred to as a tumor. This palpable or visible mass develops when malignant cells proliferate and aggregate in a confined area within a solid organ or tissue. The term “solid” refers specifically to this physical structure, which lacks cysts or significant liquid components. The initial site where this mass originates is known as the primary tumor. This structure distinguishes solid tumors, such as those found in the breast, lung, or colon, from other types of cancer that circulate freely.
Solid Versus Non-Solid Cancers
The classification of a cancer as solid or non-solid is based on where the cancerous cells originate and how they behave. Solid cancers account for approximately 80% to 90% of all diagnoses, arising from and forming a distinct, localized lump within an organ or tissue. These tumors can sometimes be detected through imaging or physical examination.
In contrast, non-solid, or hematological, cancers involve the blood, bone marrow, and lymphatic system. Examples include leukemia, lymphoma, and multiple myeloma. These conditions do not form a single, localized tumor mass but instead involve malignant cells circulating throughout the body.
The physical difference between these two categories influences the diagnostic and therapeutic approach. Solid tumors are typically assessed using imaging to locate the mass, followed by a biopsy to confirm malignancy. Non-solid cancers are diagnosed using systemic methods like blood tests and bone marrow aspirations. Solid tumors may also remain localized for a period, which often makes surgical removal a possible treatment option.
Major Tissue-Based Classifications
Solid cancers are further categorized based on the specific type of tissue from which they arise. The two most common types are carcinomas and sarcomas, which represent the vast majority of solid tumor diagnoses. Understanding this cellular origin is important because it dictates the tumor’s behavior and the most effective treatment strategy.
Carcinomas are the most prevalent type, originating in epithelial cells that line the internal and external surfaces of the body. This cell type forms the outer layer of the skin and the lining of many organs, including the breast, lungs, colon, prostate, and pancreas. Specific examples of carcinomas include adenocarcinoma, which forms in glandular tissue, and squamous cell carcinoma, which develops in flat, scale-like cells.
Sarcomas are a less common group of cancers that arise from connective or supportive tissues. These tissues include bone, muscle, fat, cartilage, and blood vessels. Osteosarcoma, a cancer of the bone, and liposarcoma, a cancer of fat cells, are examples of sarcomas.
Other solid tumors include melanomas, which originate in the pigment-producing cells of the skin, and germ cell tumors. Germ cell tumors typically arise from reproductive cells in the testes or ovaries. The specific cell type of origin determines the tumor’s classification.
Steps in Diagnosing Solid Tumors
The diagnosis of a solid tumor involves locating the mass and confirming the presence of malignant cells. The initial stage uses imaging techniques to visualize the abnormality and determine its size and location. Common tools include computerized tomography (CT) scans, magnetic resonance imaging (MRI), and positron emission tomography (PET) scans.
These scans help healthcare providers assess whether the mass has invaded nearby tissues or spread to distant sites in the body, a process known as metastasis. While imaging can suggest cancer, a definitive diagnosis requires a biopsy. A biopsy involves surgically removing a small sample of the suspicious tissue for analysis by a pathologist.
The pathologist examines the tissue under a microscope to confirm the cell type, which is necessary for classification. Following the biopsy, the cancer is assigned a grade, which describes how abnormal the cells look, and a stage, often using the TNM system, which details the size of the Tumor, involvement of lymph Nodes, and evidence of Metastasis. This classification guides the development of a treatment plan.