ERMS is the more common of two major subtypes of rhabdomyosarcoma, the other being alveolar rhabdomyosarcoma.

It has been informally classified as a "small round blue cell tumor" because of the characteristic microscopic appearance of its cells after histological staining with hematoxylin and eosin.

Sarcoma botryoides or botryoid sarcoma or botryoid rhabdomyosarcoma is a subtype of embryonal rhabdomyosarcoma, that can be observed in the walls of hollow, mucosa lined structures such as the nasopharynx, common bile duct, urinary bladder of infants and young children or the vagina in females, typically younger than age 8. The name comes from the gross appearance of "grape bunches" ("botryoid" in Greek).

In the United States, about 20-30 cases are reported each year. This may be a gross underestimate of the total number of cases as few laboratories have the reagents and expertise to make the diagnosis. The symptoms are similar to other forms of cancer and dependent on the stage. While generalized symptoms (weight loss and fatigue) may be seen, site specific symptoms are also present. If the tumor involves the head and neck region (in about 35%), then pain, a mass, obstructive symptoms, among others, may be experienced. NUT midline carcinomas are not specific to any tissue type or organ.

Common sites include the head, neck and mediastinum. The median age at diagnosis is 17 years, but older patients may be affected.

The prognosis for rhabdomyosarcoma has improved greatly in recent decades, with over 70% of patients surviving for five years after diagnosis.

Spindle cell rhabdomyosarcoma is a subtype of embryonal rhabdomyosarcoma first described by Cavazzana, Schmidt and Ninfo in 1992. This subtype has a more favorable clinical course and prognosis than usual embryonal rhabdomyosarcoma. Spindle cell rhabdomyosarcoma typically occurs in young males and most commonly occurs in paratesticular soft tissue, followed by the head and neck.

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.

For botryoid rhabdomyosarcoma of the vagina, the most common clinical finding is vaginal bleeding but vaginal bleeding is not specific for sarcoma botryoides: other vaginal cancers are possible. They may appear as a polypoid mass, somewhat yellow in color and are friable: thus, they (possibly) may break off, leading to vaginal bleeding or infections.

NUT carcinoma (formerly NUT midline carcinoma), is a rare genetically defined, very aggressive squamous cell epithelial cancer that usually arises in the midline of the body and is characterized by a chromosomal rearrangement in the nuclear protein in testis gene. In approximately 75% of cases, the coding sequence of "NUTM1" on chromosome 15q14 is fused to "BRD4" or "BRD3", which creates a chimeric gene that encodes the "BRD-NUT" fusion protein. The remaining cases, the fusion of NUTM1 is to an unknown partner gene, usually called "NUT"-variant.

Sclerosing rhabdomyosarcoma is a rare subtype of rhabdomyosarcoma that was characterized by Folpe et al. in 2002. It is microscopically characterized by primitive round cells forming microalveoli, nests, and cords in a sclerotic background.

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.

There are few early warning signs that a patient has a DSRCT. Patients are often young and healthy as the tumors grow and spread uninhibited within the abdominal cavity. These are rare tumors and symptoms are often misdiagnosed by physicians. The abdominal masses can grow to enormous size before being noticed by the patient. The tumors can be felt as hard, round masses by palpating the abdomen.

First symptoms of the disease often include abdominal distention, abdominal mass, abdominal or back pain, gastrointestinal obstruction, lack of appetite, ascites, anemia, and/or cachexia.

Other reported symptoms include unknown lumps, thyroid conditions, hormonal conditions, blood clotting, kidney or urological problems, testicle, breast, uterine, vaginal, or ovarian masses.

Childhood rhabdomyosarcoma consists of three subgroups. Embryonal is the most common among children and young adults. Alveolar and anaplastic rhabdomyosarcoma occur in the teenage years.

- Embryonal rhabdomyosarcoma develops within the first seven weeks of the embryo's development. Rapid cell growth causes masses to form along the head, neck, urinary tract, and genital organs.

- Alveolar, the second most common group, is seen later in life. During the teen years, large muscle groups come under attack, including the torso and large appendages. Aggressive treatment is needed to stop or limit progression of alveolar rhabdomyosarcoma.

- Anaplastic rhabdomyosarcoma is rarely seen in children and only precise intensive lab work can identify it.

GCNIS is seen in the following settings:

- Almost all invasive germ cell tumours of the testis in adults

- Fifty percent of patients with GCNIS developed invasive germ cell tumours within five years of initial diagnosis.

- Five percent of contralateral testes in men with a history of prior testicular germ cell tumour.

- Less than five percent of cryptorchid testes.

- Less than one percent of patients with infertility.

Clear-cell adenocarcinoma is a type of adenocarcinoma that shows clear cells.

Types include:

- Clear-cell adenocarcinoma of the vagina

- Clear-cell ovarian carcinoma

- Uterine clear-cell carcinoma

- Clear-cell adenocarcinoma of the lung (which is a type of Clear-cell carcinoma of the lung)

See also:

- Clear-cell squamous cell carcinoma of the lung

Childhood rhabdomyosarcoma is difficult to diagnose. Factors that increase the likelihood of this cancer include Li-Fraumeni syndrome, type one Neurofibromatosis, Beckwith-Wiedemann syndrome, Costello syndrome, and Noonan syndrome. Each contribute to deformations of bones, tissue, and muscles.

Endodermal sinus tumor (EST), also known as yolk sac tumor (YST), is a member of the germ cell tumor group of cancers. It is the most common testicular tumor in children under 3, and is also known as infantile embryonal carcinoma. This age group has a very good prognosis. In contrast to the pure form typical of infants, adult endodermal sinus tumors are often found in combination with other kinds of germ cell tumor, particularly teratoma and embryonal carcinoma. While pure teratoma is usually benign, endodermal sinus tumor is malignant.

Polyembryoma is a rare, very aggressive form of germ cell tumor usually found in the ovaries. Polyembryoma has features of both yolk sac tumour and undifferentiated teratoma/embryonal carcinoma, with a characteristic finding of embryoid bodies lying in a loose mesenchymal stroma.

It has been found in association with Klinefelter syndrome.

Not all germ cell tumors (GCTs) arise from "intratubular germ cell neoplasia". The following testicular GCTs do not arise from ITGCN:

- Spermatocytic seminoma

- Pediatric Yolk sac tumors (endodermal sinus tumour). This is currently an area of controversy as some authors dispute the absence of ITGCN in these cases.

- Teratoma (rare exceptions)

Embryonal carcinoma is a relatively uncommon type of germ cell tumour that occurs in the ovaries and testes.

A sarcoma is a cancer that arises from transformed cells of mesenchymal origin. Thus, malignant tumors made of cancellous bone, cartilage, fat, muscle, vascular, or hematopoietic tissues are, by definition, considered sarcomas. This is in contrast to a malignant tumor originating from epithelial cells, which are termed carcinoma. Human sarcomas are quite rare. Common malignancies, such as breast, colon, and lung cancer, are almost always carcinoma. The term is from the Greek "sarx" meaning "flesh".

In the ovary, embryonal carcinoma is quite rare, amounting to approximately three percent of ovarian germ cell tumours. The median age at diagnosis is 15 years. Symptoms and signs are varied, and may include sexual precocity and abnormal (increased, reduced or absent) uterine bleeding.

There may be elevations in serum human chorionic gonadotropin (hCG) and alpha fetoprotein (AFP) levels but it would be in association with other tumors, (e.g. yolk sac tumor) because they themselves do not produce the serum markers. At surgery, there is extension of the tumour beyond the ovary in forty percent of cases. They are generally large, unilateral tumours, with a median diameter of 17 centimetres. Long-term survival has improved following the advent of chemotherapy. The gross and histologic features of this tumour are similar to that seen in the testis.

Alveolar rhabdomyosarcoma (ARMS) is a sub-type of the rhabdomyosarcoma soft tissue cancer family whose lineage is from mesenchymal cells and are related to skeletal muscle cells. ARMS tumors resemble the alveoli tissue that can be found in the lungs. Tumor location varies from patient to patient, but is commonly found in the head and neck region, male and female urogenital tracts, the torso, and extremities. Two fusion proteins can be associated with ARMS, but are not necessary, PAX3-FKHR (now known as FOXO1). and PAX7-FKHR. In children and adolescents ARMS accounts for about 1 percent of all malignancies, has an incidence rate of 1 per million, and most cases occur sporadically with no genetic predisposition.

The histology of EST is variable, but usually includes malignant endodermal cells. These cells secrete alpha-fetoprotein (AFP), which can be detected in tumor tissue, serum, cerebrospinal fluid, urine and, in the rare case of fetal EST, in amniotic fluid. When there is incongruence between biopsy and AFP test results for EST, the result indicating presence of EST dictates treatment. This is because EST often occurs as small "malignant foci" within a larger tumor, usually teratoma, and biopsy is a sampling method; biopsy of the tumor may reveal only teratoma, whereas elevated AFP reveals that EST is also present. GATA-4, a transcription factor, also may be useful in the diagnosis of EST.

Diagnosis of EST in pregnant women and in infants is complicated by the extremely high levels of AFP in those two groups. Tumor surveillance by monitoring AFP requires accurate correction for gestational age in pregnant women, and age in infants. In pregnant women, this can be achieved simply by testing maternal serum AFP rather than tumor marker AFP. In infants, the tumor marker test is used, but must be interpreted using a reference table or graph of normal AFP in infants.

Desmoplastic small-round-cell tumor is an aggressive and rare cancer that primarily occurs as masses in the abdomen. Other areas affected may include the lymph nodes, the lining of the abdomen, diaphragm, spleen, liver, chest wall, skull, spinal cord, large intestine, small intestine, bladder, brain, lungs, testicles, ovaries, and the pelvis. Reported sites of metastatic spread include the liver, lungs, lymph nodes, brain, skull, and bones.

The tumor is classified as a soft tissue sarcoma. It is considered a childhood cancer that predominantly strikes boys and young adults. The disease rarely occurs in females, but when it does the tumors can be mistaken for ovarian cancer.

In dogs, mast cell tumors are the most frequent round cell tumor.

ARMS usually occurs in the skeletal muscle tissue of the extremities, but it is still very common in the torso, head, and neck regions. The primary tumor often presents itself as a soft mass of tissue that is painless, but the tumor can be detected if it starts to put pressure on other structures in the primary site. A large fraction of patients who are diagnosed with ARMS, roughly 25-30 percent, will have metastases at the time of diagnosis. The standard sites for metastases to form are the bone marrow, the bones, and distal nodes. Typical treatment options for patients who have been diagnosed with ARMS include standard surgery, radiation therapy, and intensive chemotherapy.