Solid Tumor Types

Solid tumors are heterotypic aggregates of many cell types, including cancer cells, cancer stem cells, connective-tissue cells, and immune cells. All of these cells can communicate with one another via specific junctions (tight and gap junction) that maintain and regulate a perfect tumor microenvironment. Several scientific studies have shown that these different genetically designed tumors with acquired resistance could control complex cell-to-cell interactions and aberrant signaling pathways leading to genome instability.

Tumor heterogeneity indicates a poor life survival prognosis. One way of categorizing solid tumors is as follows:

• Malignant
• Pre-malignant
• Benign

In cell physiology, malignant tumors, mainly of monoclonal origin, manifest six essential alterations: growth signals, intensification of anti-growth signals, cell and tissue apoptosis or necrosis, limitless replicative and proliferative potential, prolonged angiogenesis, and organ/tissue invasion followed by metastasis. The tumor's microenvironment interaction with genetics, local nutrient supply, and other organismal factors add further stochasticity.

Here is a more in-depth classification of solid malignant tumors according to the type of cell they begin to develop in:

• “in situ” invasive and metastatic carcinoma—malignancies of epithelial origin or cancerous tumors of the internal or external lining of the body. It can begin in the skin or in tissues that line or cover internal organs. There are different subtypes, including adenocarcinoma, basal cell carcinoma, squamous cell carcinoma, transitional cell carcinoma, and ductal carcinoma.
• Sarcoma and undifferentiated tumors—arise from connective or supporting tissues and can transform into soft or synovial sarcoma. Beginning sites: bone, cartilage, fat, muscle, or blood vessels (angiosarcoma, bone sarcoma, fibroblastic sarcoma, and rhabdomyosarcomas)
• Lymphoma—affects the cells of the immune system called lymphocytes; cancer begins in infection-fighting lymphocytes found in lymph nodes and spleen, e.g., Hodgkin’s disease and non-Hodgkin’s lymphomas.
• Blastoma, brain, and spinal cord cancers—blastoma develops mainly in pediatric populations. The rest of the solid tumors arise in the brain, central nervous system, or in the eye.
• Melanoma—skin malignancy. It can also form in the eyes, and, rarely, in internal organs.
• Germ cell tumors—usually arise in the ovaries and testes, but can also occur in the brain, abdomen, or chest.
• Carcinosarcoma—rare malignant solid tumors that arise in different organs and are formed by two types of cancerous cells that have the potential to metastasize: carcinoma (or epithelial cancer) and sarcoma (or connective/mesenchymal tissue cancer). It is a very aggressive biphasic solid tumor that, in most cases, appear to arise de novo.

Strict monitoring of pre-malignant tumors is important because they have the potential to change into a cancerous tumor. A consequence of the pre-malignant initiation is the production of higher quantities of matrix remodeling proteases and the release of pro-angiogenic, proliferation, and survival factors within the tumor’s microenvironment.

Benign tumors are a normal, controlled category of non-cancerous solid tumor that can form anywhere in the body. They have almost the same cellular features as the malignant ones, but they do not have the ability to travel elsewhere in the body to form metastatic sites. Even so, a benign tumor can produce damage if it compresses nearby tissue, vital organs, or blood circulation. In rare cases, such as adenoma or colon polyps, this kind of tumor has the capacity to transition to a malignant state.

Benign tumors can be classified by:

• The type of extracellular matrix production
• The type of cells
• Fibrous and connective tissue of any organ
• Localization on the blood vessels