Most cases of SPB progress to multiple myeloma within 2–4 years of diagnosis, but the overall median survival for SPB is 7–12 years. 30–50% of extramedullary plasmacytoma cases progress to multiple myeloma with a median time of 1.5–2.5 years. 15–45% of SPB and 50–65% of extramedullary plasmacytoma are disease free after 10 years.

Plasmacytomas are a rare form of cancer. SPB is the most common form of the disease and accounts for 3-5% of all plasma cell malignancies. The median age at diagnosis for all plasmacytomas is 55. Both SPB and extramedullary plasmacytoma are more prevalent in males; with a 2:1 male to female ratio for SPB and a 3:1 ratio for extramedullary plasmacytoma.

The disease has been reported to affect 3 per 1000 infants younger than 6 months in the United States. No predilection by race or sex has been established. Almost all cases occur by the age of 5 months. The familial form is inherited in an autosomal dominant fashion with variable penetrance. The familial form tends to have an earlier onset and is present at birth in 24% of cases, with an average age at onset of 6.8 weeks. The average age at onset for the sporadic form is 9–11 weeks.

Cortical hyperostosis is a potential side effect of long-term use of prostaglandins in neonates.

Undifferentiated pleomorphic sarcoma is regarded as the most common soft tissue sarcoma of late adult life. It rarely occurs in children. It occurs more often in Caucasians than in those of African or Asian descent and is a male-predominant disease, afflicting two males for every female.

Treatment is mainly surgical; radiotherapy or chemotherapy is usually an indication of relapse. Head and neck desmoid fibromatosis is a serious condition due to local aggression, specific anatomical patterns and the high rate of relapse. For children surgery is particularly difficult, given the potential for growth disorders.

Treatment includes prompt radical excision with a wide margin and/or radiation. Despite their local infiltrative and aggressive behavior, mortality is minimal to nonexistent for peripheral tumours. In intra-abdominal fibromatosis associated with Familial adenomatous polyposis (FAP), surgery is avoided if possible due to high rates of recurrence within the abdomen carrying significant morbidity and mortality. Conversely, for intra-abdominal fibromatosis without evidence of FAP extensive surgery may still be required for local symptoms, but the risk of recurrence is low.

Prognosis depends on the primary tumor grade (appearance under the microscope as judged by a pathologist), size, resectability (whether it can be completely removed surgically), and presence of metastases. The five-year survival is 80%.

Globally, multiple myeloma affected 488,000 people and resulted in 101,100 deaths in 2015. This is up from 49,000 in 1990.

Subtypes of fibromatosis include -

- Juvenile fibromatosis

- Fibromatosis colli: Non-neoplastic sternocleidomastoid muscle enlargement in early infancy. Does not generally require resection and responds well to physiotherapy.

- Infantile digital fibromatosis

- Infantile myofibromatosis

- Ipofibromatosis

- Fibromatosis hyalinica multiplex

- Plantar fibromatosis

- Penile fibromatosis (Peyronie's disease)

- Palmar fibromatosis (Dupuytren's contracture)

Soft-tissue sarcomas are relatively uncommon cancers. They account for less than 1% of all new cancer cases each year. This may be because cells in soft tissue, in contrast to tissues that more commonly give rise to malignancies, are not continuously dividing cells.

In 2006, about 9,500 new cases were diagnosed in the United States. Soft-tissue sarcomas are more commonly found in older patients (>50 years old) although in children and adolescents under age 20, certain histologies are common (rhabdomyosarcoma, synovial sarcoma).

Around 3,300 people were diagnosed with soft tissue sarcoma in the UK 2011.

ASPS is an extremely rare cancer. While sarcomas comprise about 1% of all newly diagnosed cancers, and 15% of all childhood cancers, ASPS comprises less than 1% of sarcomas. According to the American Cancer Society, about 9530 new cases of soft tissue sarcoma will be diagnosed in the USA in 2006. This predicts under 100 new cases of ASPS. Such low numbers of occurrence seriously impede the search for a cure by making it hard to gather any meaningful statistics about the disease. As a result, finding the best treatment option often involves making a lot of educated guesses.

Most soft-tissue sarcomas are not associated with any known risk factors or identifiable cause. There are some exceptions:

- Studies suggest that workers who are exposed to chlorophenols in wood preservatives and phenoxy herbicides may have an increased risk of developing soft-tissue sarcomas. An unusual percentage of patients with a rare blood vessel tumor, angiosarcoma of the liver, have been exposed to vinyl chloride in their work. This substance is used in the manufacture of certain plastics, notably PVC.

- In the early 1900s, when scientists were just discovering the potential uses of radiation to treat disease, little was known about safe dosage levels and precise methods of delivery. At that time, radiation was used to treat a variety of noncancerous medical problems, including enlargement of the tonsils, adenoids, and thymus gland. Later, researchers found that high doses of radiation caused soft-tissue sarcomas in some patients. Because of this risk, radiation treatment for cancer is now planned to ensure that the maximum dosage of radiation is delivered to diseased tissue while surrounding healthy tissue is protected as much as possible.

- Kaposi's sarcoma, a rare cancer of the cells that line blood vessels in the skin and mucus membranes, is caused by Human herpesvirus 8. Kaposi's sarcoma often occurs in patients with AIDS (acquired immune deficiency syndrome). Kaposi's sarcoma, however, has different characteristics than typical soft-tissue sarcomas and is treated differently.

- In a very small fraction of cases, sarcoma may be related to a rare inherited genetic alteration of the p53 gene and is known as Li-Fraumeni syndrome. Certain other inherited diseases are associated with an increased risk of developing soft-tissue sarcomas. For example, people with neurofibromatosis type I (also called von Recklinghausen's disease, associated with alterations in the NF1 gene) are at an increased risk of developing soft-tissue sarcomas known as malignant peripheral nerve sheath tumors. Patients with inherited retinoblastoma have alterations in the RB1 gene, a tumor suppressor gene, and are likely to develop soft-tissue sarcomas as they mature into adulthood.

Myeloma is the 17th most common cancer in the UK (around 4,800 people were diagnosed with the disease in 2011), and it is the 16th most common cause of cancer death (around 2,700 people died of it in 2012).

This is an uncommon lesion, usually affecting young patients (mean age, 30 years), with a male to female ratio of 2:1. The middle ear is involved, although it may extend to the external auditory canal if there is tympanic membrane perforation.

Work out of Huntsman Cancer Institute (HCI) in Utah has demonstrated that ASPS might be driven in part by lactate both being used as a fuel and driving angiogenesis.

Embryonal rhabdomyosarcoma (ERMS) is a rare histological form of cancer of connective tissue wherein the mesenchymally-derived malignant cells resemble the primitive developing skeletal muscle of the embryo. It is the most common soft tissue sarcoma occurring in children.

Malignant fibrous cytoma is a soft tissue sarcoma that usually occurs in the limbs, most commonly the legs, and may also occur in the abdomen. Also called malignant fibrous histiocytoma.

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

Most frequent in middle-aged and older adults (age 40 and above), liposarcomas are the second most common of all soft-tissue sarcomas following malignant fibrous histiocytomas. Annually 2.5 cases occur per million population.

A synovial sarcoma (also known as: malignant synovioma) is a rare form of cancer which occurs primarily in the extremities of the arms or legs, often in close proximity to joint capsules and tendon sheaths. As one of the soft tissue sarcomas, it is one of the rarest forms of soft tissue cancer.

The name "synovial sarcoma" was coined early in the 20th century, as some researchers thought that the microscopic similarity of some tumors to synovium, and its propensity to arise adjacent to joints, indicated a synovial origin; however, the actual cells from which the tumor develops are unknown and not necessarily synovial.

Primary synovial sarcomas are most common in the soft tissue near the large joints of the arm and leg but have been documented in most human tissues and organs, including the brain, prostate, and heart.

Synovial sarcoma occurs most commonly in the young, representing

about 8% of all soft tissue sarcomas but about 15–20% of cases occur in adolescents and young adults. The peak of incidence is in the third decade of life, with males being affected more often than females (ratio around 1.2:1).

Myopericytoma, also glomangiopericytoma, is a rare perivascular soft tissue tumour. It is usually benign and typically in the distal extremities.

It is thought to overlap with myofibroma.

Glomangiosarcoma is a low grade tumor of the soft tissue. They rarely metastasize, but metastases are possible. It is also known as "malignant glomus tumor". Positive staining for vimentin has been reported.

Infantile cortical hyperostosis is a self-limited condition, meaning that the disease resolves on its own without treatment, usually within 6–9 months. Long-term deformities of the involved bones, including bony fusions and limb-length inequalities, are possible but rare.

Clear cell sarcoma of the kidney (CCSK) is an extremely rare type of kidney cancer comprising 3% of all pediatric renal tumours. Clear cell sarcoma of the kidney can spread from the kidney to other organs, most commonly the bone, but also including the lungs, brain, and soft tissues of the body.

Despite the similarities in names, "clear cell sarcoma of the kidney" is unrelated to clear cell sarcoma of soft tissue, also known as malignant melanoma of soft parts.

The cause of the rare condition of tumoral calcinosis is not entirely understood. It is generally characterized by large, globular calcifications near joints.

An otic polyp (also called aural polyp) is a benign proliferation of chronic inflammatory cells associated with granulation tissue, in response to a longstanding inflammatory process of the middle ear.