RMS can occur in almost any soft-tissue site in the body; the most common primary sites are genitourinary (24%), parameningeal (16%), extremity (19%), orbit (9%), other head and neck (10%), and miscellaneous other sites (22%). RMS often presents as a mass, but signs and symptoms can vary widely depending on the site of the primary tumor. Genitourinary tumors may present with hematuria, urinary tract obstruction, and/or a scrotal or vaginal mass. Tumors that arise in the retroperitoneum and mediastinum can become quite large before producing signs and symptoms. Parameningeal tumors may present with cranial nerve dysfunction, symptoms of sinusitis, ear discharge, headaches, and facial pain. Orbital tumors often present with orbital swelling and proptosis. Extremity tumors generally present as a rapidly enlarging, firm mass in the relevant tissue. The cancer's prevalence in the head, face, and neck will often allow for earlier signs of the disease simply due to the obvious nature of tumors in these locations. Despite the varying presentation and typically aggressive nature of the disease, RMS has the potential to be diagnosed and treated early. The fourth IRSG study found that 23% of patients were diagnosed in time for a complete resection of their cancer, and 15% had resection with only minimal remnants of the diseased cells.

A myxoid liposarcoma is a malignant adipose tissue neoplasm of myxoid appearance histologically.

Myxoid liposarcomas are the second most common type of liposarcoma, representing 30–40% of all liposarcomas in the limbs; occurring most commonly in the legs, particularly the thigh, followed by the buttocks, retroperitoneum, trunk, ankle, proximal limb girdle, head and neck, and wrist. They occur in the intermuscular fascial planes or deep-seated areas. They present as a large, slow-growing, painless mass.

They are associated with a fusion between DDIT3 or "CHOP" (at 12q13.1-q13.2) and FUS or "TLS" (at 16p11.2) or EWS (at 22q12.2).

The specific translocation of FUS-DDIT3 is t(12;16)(q13;p11).

Leiomyosarcoma, also referred to as LMS, is a malignant (cancerous) smooth muscle tumor. A benign tumor originating from the same tissue is termed leiomyoma. It is also important to note that while it has been believed that leiomyosarcomas do not arise from leiomyomas, there are leiomyoma variants for which classification is evolving.

About 1 person in 100,000 gets diagnosed with LMS each year. Leiomyosarcoma is one of the more common types of soft-tissue sarcoma, representing 10 percent to 20 percent of new cases. (Leiomyosarcoma of the bone is more rare.) Sarcoma is rare, consisting of only 1 percent of cancer cases in adults. Leiomyosarcomas can be very unpredictable. They can remain dormant for long periods of time and recur after years. It is a resistant cancer, meaning generally not very responsive to chemotherapy or radiation. The best outcomes occur when it can be removed surgically with wide margins early, while small and still in situ.

Smooth muscle cells make up the involuntary muscles, which are found in most parts of the body, including the uterus, stomach and intestines, the walls of all blood vessels, and the skin. It is therefore possible for leiomyosarcomas to appear at any site in the body. They are most commonly found in the uterus, stomach, small intestine and retroperitoneum.

Uterine leiomyosarcomas come from the smooth muscle in the muscle layer of the uterus. Cutaneous leiomyosarcomas derive from the pilo-erector muscles in the skin. Gastrointestinal leiomyosarcomas might come from smooth muscle in the GI tract or, alternatively, also from a blood vessel. At most other primary sites—retroperitoneal extremity (in the abdomen, behind the intestines), truncal, abdominal organs, etc.—leiomyosarcomas appear to grow from the muscle layer of a blood vessel (the tunica media). Thus a leiomyosarcoma can have a primary site of origin anywhere in the body where there is a blood vessel.

The tumors are usually hemorrhagic and soft and microscopically marked by pleomorphism, abundant (15–30 per 10 high power fields) abnormal mitotic figures, and coagulative tumor cell necrosis. There is a wide differential diagnosis, which includes spindle cell carcinoma, spindle cell melanoma, fibrosarcoma, malignant peripheral nerve sheath tumor and even biphenotypic sinonasal sarcoma.

Patients usually note a deep seated mass in their soft tissue. Only when the tumor is very large do symptoms of pain or functional disturbances occur.

Retroperitoneal tumors may present themselves with signs of weight loss and emaciation and abdominal pain. These tumors may also compress the kidney or ureter leading to kidney failure.

MTSCC has a gross appearance close to papillary RCC. Microscopically, it has three histologic components: mucin, tumor cells forming tubules, and spindle cells. It is characterized by the proliferation of cuboidal and spindle cells arranged in tubular or sheet-like arrays, typically with a mucinous or myxoid background.

Mucinous tubular and spindle cell carcinoma (MTSCC) is a rare subtype of renal cell carcinoma (RCC), that is included in the 2004 WHO classification of RCC. MTSCC is a rare neoplasm and is considered as a low-grade entity. It may be a variant of papillary RCC. This tumor occurs throughout life (age range 17–82 years) and is more frequent in females.

Liposarcoma is a cancer that arises in fat cells in deep soft tissue, such as that inside the thigh or in the retroperitoneum. Liposarcoma is a rare type of cancer that bears a resemblance to fat cells when examined under a microscope.

They are typically large bulky tumors, and tend to have multiple smaller satellites that extend beyond the main confines of the tumor.

Liposarcomas, like all sarcomas, are rare.

Hemangiopericytoma located in the cerebral cavity is an aggressive tumor of the Mesenchyme with oval nuclei with scant cytoplasm. "There is dense intercellular reticulin staining. Tumor cells can be fibroblastic, myxoid, or pericytic. These tumors, in contrast to meningiomas, do not stain with epithelial membrane antigen. They have a grade 2 or 3 biological behavior, and need to be distinguished from benign meningiomas because of their high rate of recurrence (68.2%) and metastases (Maier et al. 1992; Kleihues et al. 1993 )."

Individuals presenting with fibrosarcoma are usually adults aged thirty to fifty five years, often presenting with pain. In adults, males have a higher incidence for fibrosarcoma than females.

Fibrosarcoma (fibroblastic sarcoma) is a malignant mesenchymal tumour derived from fibrous connective tissue and characterized by the presence of immature proliferating fibroblasts or undifferentiated anaplastic spindle cells in a storiform pattern. It is usually found in males aged 30 to 40 . It originates in fibrous tissues of the bone and invades long or flat bones such as femur, tibia, and mandible. It also involves periosteum and overlying muscle.

Myosarcoma is a malignant muscle tumor. People with myosarcoma often wake up with the feeling as if they had a cramp during their sleep.

Leiomyosarcoma is sarcoma of smooth muscle, and rhabdomyosarcoma is sarcoma of striated muscle. However, the term myosarcoma itself still appears in the literature.

A hemangiopericytoma (HPC) is a type of soft tissue sarcoma that originates in the pericytes in the walls of capillaries. When inside the nervous system, although not strictly a meningioma tumor, it is a meningeal tumor with a special aggressive behavior. It was first characterized in 1942.

Given the difficulty in diagnosing rhabdomyosarcoma, definitive classification of subsets has proven difficult. As a result, classification systems vary by institute and organization. However, rhabdomyosarcoma can be generally divided into three histological subsets:

- "Embryonal rhabdomyosarcoma" (ERMS) is the most common histological variant, comprising approximately 60–70% of childhood cases. It is most common in children 0–4 years old, with a maximum reported incidence of 4 cases per 1 million children. ERMS is characterized by spindle-shaped cells with a stromal-rich appearance, and the morphology is similar to the developing muscle cells of a 6–8 week old embryo. Tumors often present in the head and neck as well as the genitourinary tract. ERMS also has two defined subtypes, botryoid and spindle cell ERMS, and these subtypes are associated with a favorable prognosis.

- Subtypes of ERMS

- Botryoid ERMS is almost always found in mucosal lined organs including the vagina, bladder, and nasopharynx (although presentation in the nasopharynx typically affects older children). It often presents in patients <1 year old as a round, grape-like mass on the affected organ. Histologically, cells of the botryoid variant are defined by a dense tumor layer under an epithelium (cambium layer).

- Spindle cell rhabdomyosarcoma comprises about 3% of all RMS cases. This subtype is very similar to that of leiomyosarcoma (cancer of the smooth muscle tissue), and it has a fascicular, spindled, and leiomyomatous growth pattern with notable rhabdomyoblastic differentiation . It occurs most commonly in the paratesticular region, and the prognosis for this particular form of RMS is excellent with a reported 5 year survival rate of 95%.

- "Alveolar rhabdomyosarcoma" (ARMS) is the second most common type. ARMS comprises approximately 20–25% of RMS-related tumors, and it is equally distributed among all age groups with an incidence of about 1 case per 1 million people ages 0 to 19. For this reason, it is the most common form of RMS observed in young adults and teenagers, who are less prone to the embryonal variant. This type of RMS is characterized by densely-packed, round cells that arrange around spaces similar in shape to pulmonary alveoli, although variants have been discovered without these characteristic alveolar spacings. ARMS tends to form more often in the extremities, trunk, and peritoneum. It is also typically more aggressive than ERMS.

- "Anaplastic (undifferentiated) rhabdomyosarcoma", also known as "pleomorphic rhabdomyosarcoma", is the final variant of RMS recognized in most classification systems. Anaplastic rhabdomyosarcoma is defined by the presence of anaplastic cells with large, lobate hyperchromatic nuclei and multipolar mitotic figures. These tumors display high heterogeneity and extremely poor differentiation. The anaplastic cells may be diffuse or localized, with the diffuse variation correlating to a worse prognosis. It occurs most often in adults, rarely in children, and is often discovered in the extremities. Due to the lack of discernible separation among cancers of this type, clinicians will often label undiagnosed sarcomas with little to no discernible features as anaplastic RMS. It is the most aggressive type of RMS, and will often require intensive treatment.

There is also an extremely rare subtype of RMS that has been described as "sclerosing rhabdomyosarcoma" by "Folpe, et al", but it is not a currently recognized subtype by the NCI or WHO. This subtype has characteristic histology involving hyaline sclerosis and pseudovascular development. Its origins are unclear, but some studies have pointed to an association with embryonal RMS.

Multiple classification systems have been proposed for guiding management and treatment, and the most recent and widely used classification system is the "International Classification of Rhabdomyosarcoma" or ICR. It was created by the IRSG in 1995 after their series of four multi-institutional trials aimed at studying the presentation, histology, epidemiology, and treatment of RMS (IRSG I–IV). The ICR system is based on prognostic indicators identified in IRSG I–IV. Pleomorphic rhabdomyosarcoma usually occurs in adults rather than children, and is therefor not included in this system. Sclerosing rhabdomyosarcoma is also not included in this system due to its rare presentation and weak classification schema.

Almost all women present with uterine fibroids, approximately 76% with dermal manifestations and 10-16% with renal tumors.

The uterine fibroids tend to occur at younger age and larger and more numerous than in general population. They may be distinguishable from sporadic fibroids by special histological features such as prominent nucleoli with perinucleolar halos.

The skin presentation is of asymmetrical, reddish-brown nodules or papules with a firm consistency, predominantly located on the limbs (multiple cutaneous leiomyoma), although they may occur anywhere, including the face. The lesions, which are typically painful and most often present during the third decade of life, are piloleiomyomata—a benign smooth muscle tumour arising from the arrectores pilorum muscles of the skin. These tumours may also arise in the tunica dartos of the scrotum and the mammillary muscle of the nipple (genital leiomyoma), the smooth muscle of blood vessels (angioleiomyoma) and the lung (pulmonary lymphangioleiomyomatosis). A pseudo-Darier sign may be present.

The renal cell carcinoma tends to be of the papillary (type 2) form and tends to occur more commonly in women than men with this syndrome. These cancers present earlier than is usual for renal cell carcinomas (typically in the twenties and thirties) and to be at relatively advanced stages at presentation. Tumours have rarely been reported in children. These tumours occur in ~20% of those with this mutation suggesting that other factors are involved in the pathogenesis.

The tumor is usually solitary and presents as a slow growing, painless, firm single nodular mass. Isolated nodules are generally outgrowths of the main nodule rather than a multinodular presentation. It is usually mobile unless found in the palate and can cause atrophy of the mandibular ramus when located in the parotid gland. When found in the parotid tail, it may present as an eversion of the ear lobe. Though it is classified as a benign tumor, pleomorphic adenomas have the capacity to grow to large proportions and may undergo malignant transformation, to form carcinoma ex-pleomorphic adenoma, a risk that increases with time (9.5% chance to convert into malignancy in 15 years). Although it is "benign" the tumor is aneuploid, it can recur after resection, it invades normal adjacent tissue and distant metastases have been reported after long (+10 years) time intervals.

Pleomorphic adenoma is a common benign salivary gland neoplasm characterised by neoplastic proliferation of parenchymatous glandular cells along with myoepithelial components, having a malignant potentiality. It is the most common type of salivary gland tumor and the most common tumor of the parotid gland. It derives its name from the architectural Pleomorphism (variable appearance) seen by light microscopy. It is also known as "Mixed tumor, salivary gland type", which describes its pleomorphic appearance as opposed to its dual origin from epithelial and myoepithelial elements.

Myxoid lipoblastoma is a cutaneous condition characterized by excess mucin. It resembles myxoid liposarcoma.

Trichoepithelioma is a neoplasm of the adnexa of the skin. Its appearance is similar to basal cell carcinoma.

One form has been mapped to chromosome 9p21.

Typically patients present with progressive pain, often long standing and/or bony swelling and restricted range of movement in affected limb 3,12. The latter is most often the case in bones with little overlying soft tissues (e.g. short tubular bones of the hands and feet).

Most chondromyxoid fibromas are located in the metaphyseal region of long bones (60%), and may extend to the epiphyseal line and even rarely abut the articular surface 3,12. They are almost never just epiphyseal 3. The classical site is the upper 1/3rd of tibia ( which accounts for 25% of all cases) with the small tubular bones of the foot, the distal femur and pelvis being other relatively common locations 12.

Rarely occur in the skull or skull base.

Patients present with a slow-growing, painless, solitary mass, usually of the subcutaneous tissues. It is much less frequently noted in the intramuscular tissue. It is not uncommon for symptoms to be present for years.

Benign neoplasm with "BROWN FAT" is noted.

Lipoblastoma is a type of subcutaneous benign fatty tumor.

Types include:

- Benign lipoblastomatosis, a tumor, also known as an embryonic lipoma, which usually occurs in children under three years old. This is the tumor of brown fat cells.

- Myxoid lipoblastoma, a cutaneous condition characterized by excess mucin

Myxoid chondrosarcoma is a type of Chondrosarcoma.

It has been associated with a t(9;22) (q22;q12) EWS/CHN gene fusion.

Smooth muscle tumor of uncertain malignant potential, abbreviated STUMP, is an uncommon tumor of the uterine smooth muscle that may behave like a benign tumor or a cancerous tumor.

This tumor should not be confused with the prostatic stromal tumor of uncertain malignant potential which may be abbreviated the same way ("STUMP").

The Bell criteria were developed to help categorize them and differentiate them from their main differential diagnoses, leiomyosarcoma and uterine leiomyoma.

This lesion has been called a fetal lipoma, lipoma of embryonic fat or a lipoma of immature fat.