Introduction:
When cells in the human body divide rapidly, they form masses known as tumors. Tumors are classified into cancerous (malignant) and non-cancerous (benign). The primary delineating factor in the case of a cancerous tumor is its ability to spread and invade surrounding and distant organs. A tumor can originate from any cells or tissues in the body. The consequences of the tumor mainly depend on its origin, size, nature, and location.
What Are Mesenchymal Tumors?
Mesenchymal tumors are simply tumors developing from mesenchymal tissues. Therefore, understanding mesenchymal tissue is essential in recognizing different types of tumors.
Mesenchymal Cells and Tissues:
Mesenchyme is a tissue found in animals comprising loosely arranged cells in a matrix made of proteins and fluid. These cells are multipotent and are capable of giving rise to supportive structures of the body. These cells account for the majority of the body’s bulk and mainly include:
1. Fibroblasts: The cells that form the structural framework of other tissues.
2. Adipocytes: The fat tissue cells.
3. Myoblasts: The cells that form skeletal, cardiac, or smooth muscles.
4. Endothelium Cells: The cells lining the blood vessels.
5. Miscellaneous: The nerve cells, bone-forming cells (osteoblasts), immune cells, etc.
Mesenchymal Tumors:
Mesenchymal tumors originate from any of the cells mentioned above. They are also called soft tissue tumors and connective tissue tumors. Any organ can develop a mesenchymal tumor with a different incidence rate. Interestingly, connective tissue tumors are higher in cats and dogs. The malignant mesenchymal tumors are aggressive as the cells have a higher ability to differentiate. Malignant soft tissue tumors are addressed with the “sarcoma” suffix.
What Causes the Development of Mesenchymal Tumors?
The reason behind the occurrence of soft tissue tumors remains a mystery. However, studies have shown the influence of some risk factors. For example, people are more likely to develop soft tissue tumors if mutations in their DNA (deoxyribonucleic acid). In addition, mutations in the DNA or gene that code for proteins controlling cell division can lead to tumor development. Having a family history of soft tissue tumors also increases the risk. On the other hand, most mesenchymal tumors develop without any apparent risk factors.
What Are the Types of Mesenchymal Tumors?
A. Fibrous Tissue Tumors: Tumors originate from connective tissue cells called fibroblasts. Fibroblasts produce collagen that makes the structural framework of muscles, bones, cartilages, ligaments, etc.
Benign Tumors:
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Fibroma: They are benign round or oval masses that are well encapsulated. Fibromas are hard or soft to touch and often develop on or beneath the skin.
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Collagenous Hamartoma: A rare benign tumor characterized by a mass consisting of abundant collagen, fibrous tissue, and keratin-filled cysts.
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Nodular Fasciitis: A non-cancerous skin growth due to muscle fibers (fascia) inflammation. It is a rare yet aggressive tumor that commonly occurs in the upper body.
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Myxoma: This is a benign myxoid-type (connective tissue composed of mucous-like material) tumor composed of primitive connective tissue cells. This tumor is rare and develops as a nodule in the heart musculature.
Malignant Tumors:
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Fibrosarcoma: A rare cancerous soft tissue tumor of the fibroblasts. It develops in adults between 20 years to 60 years of age.
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Myxosarcoma: A tumor similar to myxoma but cancerous. Myxosarcoma is usually difficult to operate on and often spreads to the lungs.
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Malignant Fibrous Histiocytoma: Cancer that develops in the soft tissues and sometimes in bones. It commonly occurs in the legs, arms, and back with a preference for distant spread.
B. Fat (Adipose) Tissue Tumors: These are the masses that originate from adipocytes, the cells that store fat.
Benign Tumors:
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Lipoma: This is a benign, soft-tissue tumor that usually grows below the skin and muscles. The tumor feels like a small lump and remains asymptomatic (in majority of the cases).
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Angiolipoma: This is a benign tumor similar to a lipoma that contains blood vessels. Angiolipomas can cause pain and sometimes infiltrate the surrounding tissues.
Malignant Tumors:
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Liposarcoma: Cancerous variant of lipoma that invades the surrounding tissues and recurs at the original site. The severity of liposarcoma depends on the stage and subtype of the tumor.
C. Smooth Muscle Tumors: Most smooth muscle (muscles present in the hollow organs including the blood vessels, intestines, uterus, etc.) tumors are rare and benign in nature. They show smooth muscle differentiation.
Benign Tumors:
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Leiomyoma: Benign tumors originating from smooth muscle fibers, and they commonly occur in the intestines and female genitals. It is a slow-progressing tumor that can be surgically removed.
Malignant Tumors:
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Leiomyosarcoma: A rare yet aggressive cancer of the smooth muscles that grow in the abdomen or uterus (commonly).
D. Skeletal Muscle Tumors: Sarcomas (cancerous) of the skeletal muscles commonly occur compared to benign tumors. Skeletal muscles are voluntary and are responsible for body movements. These tumors can develop extra muscular (outside the muscles) or in the bones.
Benign Tumors:
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Rhabdomyoma: This is a benign tumor that shows skeletal muscle differentiation. Rhabdomyomas can occur in the heart (cardiac) or outside the heart (extracardiac). Cardiac rhabdomyosarcomas are common in children.
Malignant Tumors:
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Rhabdomyosarcoma: This is a cancerous tumor of the skeletal muscles that can occur in any part of the body. Usually, the muscles attached to the bones tend to develop rhabdomyosarcomas. It is common in childhood, and certain genetic conditions increase the risk of rhabdomyosarcomas.
E. Vascular Tumors: These are soft tissue tumors that begin from the blood vessels or lymphatic vessels. They can be simple malformations or cancerous growths (in rare cases).
Benign Tumors:
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Hemangioma: This is a benign growth developing from the cells of blood vessels (endothelial cells). It commonly occurs on the face, neck, and back. Hemangiomas can be congenital (present at birth) or acquired during a lifetime.
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Lymphangioma: These benign malformations are tumors of the lymphatic system. It is an uncommon tumor that can develop anywhere on the skin or mucous membrane. Lymphangiomas can be superficial or deep, depending on their depth from the skin surface. They are either congenital or acquired.
Malignant Tumors:
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Hemangiosarcoma: The cancerous version of blood vessel tumors is extremely rare in humans and often occurs along with an underlying genetic condition. It is an aggressive and locally invasive tumor and has been associated with vinyl chloride toxicity.
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Lymphangiosarcoma: This is a rare cancer that usually occurs in the extremities. Lymphaniosarcomas present with a discoloration of the skin, painful nodules and progresses to form an ulcer with superficial crusting.
F. Nerve Cell Tumors: Nerve tumors originate from the nerves arising from the brain or spinal cord (peripheral nerves). Most of these are non-cancerous and grow slowly. However, malignant nerve tumors are aggressive and need extensive treatment.
Benign Tumors:
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Traumatic Neuroma: This is a common disorder occurring in the peripheral nerves that usually develops post-trauma or surgery. The tumor looks like a firm nodule and contains an abnormal mass of nerve cells.
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Neurofibroma: Common benign growths of the nerve cells that can occur beneath the skin. These cases can occur independently or be associated with genetic disorders (neurofibromatosis). They often cause pain and itching.
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Schwannoma: Schwann cells (cells that form the protective layer of nerves) can rarely give rise to benign masses. They can occur anywhere in the body, and the symptoms mainly depend on the affected organ.
Malignant Tumors:
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Neurofibrosarcoma: These are rare malignant tumors of the peripheral nerves. It commonly occurs in the arms, legs, lower back, and neck. Neurofibrosarcomas develop along with the course of the nerve and rarely spread to other organs.
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Malignant Schwannoma: Under rare circumstances, a schwannoma can become cancerous. They spontaneously occur in adults and sometimes can be associated with a genetic condition called neurofibromatosis type 1.
What Is the General Treatment Protocol for Mesenchymal Tumors?
Benign Soft Tissue Tumors: Surgical management is the treatment of choice for benign tumors. However, if these tumors are not causing any discomfort, doctors wait and observe. If surgery is carried out, the goal should be to minimize the damage to surrounding structures.
Malignant Soft Tissue Tumors: Depending on the type, extent, and aggressiveness of cancer, the doctor may advise surgery, radiotherapy, chemotherapy, and immunotherapy. Individual treatment can be carried out, or a combination of multiple methods can be used.
Conclusion:
Mesenchymal tumors are simply tumors developing from mesenchymal tissues. These tissues are made of cells like fibroblasts, nerve cells, blood vessel cells, muscle cells, etc. Benign soft tissues are common in humans, but cancerous mesenchymal tumors are rare. Many tumors can originate from various cells, and the treatment mainly depends on the tumor's type, severity, and aggressiveness.
