Uterine fibroids are leiomyomata of the uterine smooth muscle. As other leiomyomata, they are benign, but may lead to excessive menstrual bleeding (menorrhagia), often cause anemia and may lead to infertility.

A rare form of these tumors is uterine lipoleiomyoma—benign tumors consisting of a mixture of adipocytes and smooth muscle cells. Uterine lipoleiomyomata have been observed together with ovarian and other pathologies and some of them may develop into liposarcoma. These tumors are monoclonal, and non-random chromosomal abnormalities have been seen in 40% of the tumors.

Mesenchymal neoplasms of the gallbladder are rare and in particular leiomyomas of the gallbladder have been rarely reported, all of them in patients with immune system disorders. Although, recently, a case was reported in absence of associated immunodeficiency at Monash Hospital in Melbourne Australia in a healthy 39-year-old woman with no symptoms.

Benign metastasizing leiomyoma is a rare condition characterized by the growth of uterine leiomyoma in the other regions especially the lungs.

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.

Intravenous leiomyomatosis is a rare condition seen exclusively in women in which leiomyomata, benign smooth muscle tumors, are found in veins. The masses are benign-appearing but can spread throughout the venous system leaving the uterus and even cause death when growing into the heart from the IVC. While the possibility that these arose de novo from the smooth muscle in the blood vessel wall was considered, chromosomal analysis suggests a uterine origin. Intravenous leiomyomata are usually but not always associated with uterine fibroids, and tend to recur.

This condition is related to benign metastasizing leiomyoma, in which the masses appear in more distant locations such as the lung and lymph nodes.

IFPs consist of spindle cells that are concentrically arranged around blood vessels and have inflammation, especially eosinophils.

They may have leiomyoma/schwannoma-like areas with nuclear palisading.

They typically stain with CD34 and vimentin, and, generally, do not stain with CD117 and S100.

The endoscopic differential diagnosis includes other benign, pre-malignant and malignant gastrointestinal polyps.

Inflammatory fibroid polyp, abbreviated IFP, is a benign abnormal growth of tissue projecting into the lumen of the gastrointestinal tract.

Reed’s syndrome (or familial leiomyomatosis cutis et uteri) is a rare inherited condition characterised by multiple cutaneous leiomyomas and, in women, uterine leiomyomas. It predisposes for renal cell cancer, an association denominated hereditary leiomyomatosis and renal cell cancer, and it is also associated with increased risk of uterine leiomyosarcoma. The syndrome is caused by a mutation in the fumarate hydratase gene, which leads to an accumulation of fumarate. The inheritance pattern is autosomal dominant.

Mucinous cystadenomas may be found in the:

- Ovary - ovarian mucinous cystadenoma

- Pancreas - pancreatic mucinous cystadenoma

- Peritoneum - peritoneal mucinous cystadenoma

- Liver - mucinous cystadenoma of the liver

- Vermiform appendix - appendiceal mucinous cystadenoma (see cystadenoma)

To remove the tumor from the body, a myomectomy or hysterectomy is often required.

Mucinous cystadenoma is a benign cystic tumor lined by a mucinous epithelium. It is a type of cystic adenoma (cystadenoma).

Mucinous cystadenoma may arise in a number of locations; however, mucinous cystadenoma at different locations are not generally considered to be related to one another.

Signs and symptoms of pseudomyxoma peritonei may include abdominal or pelvic pain and/or bloating, distension, digestive disorders, weight changes, increased girth, and infertility.

They are of two types.

- The leiomyoma occurs in the skin or gut but the common form is the uterine fibroid.

- Rhabdomyomas are rare tumors of muscles, they occur in childhood and often become malignant.

The uterine sarcomas form a group of malignant tumors that arises from the smooth muscle or connective tissue of the uterus.

Pseudomyxoma peritonei (PMP) is a clinical condition caused by cancerous cells (mucinous adenocarcinoma) that produce abundant mucin or gelatinous ascites. The tumors cause fibrosis of tissues and impede digestion or organ function, and if left untreated, the tumors and mucin they produce will fill the abdominal cavity. This will result in compression of organs and will destroy the function of colon, small intestine, stomach, or other organs. Prognosis with treatment in many cases is optimistic, but the disease is lethal if untreated, with death by cachexia, bowel obstruction, or other types of complications.

This disease is most commonly caused by an appendiceal primary cancer (cancer of the appendix); mucinous tumors of the ovary have also been implicated, although in most cases ovarian involvement is favored to be a metastasis from an appendiceal or other gastrointestinal source. Disease is typically classified as low- or high-grade (with signet ring cells). When disease presents with low-grade histologic features the cancer rarely spreads through the lymphatic system or through the bloodstream.

Angioleiomyoma (vascular leiomyoma, angiomyoma) of the skin is thought to arise from vascular smooth muscle, and is generally acquired.

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.

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.

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.

Unusual or postmenopausal bleeding may be a sign of a malignancy including uterine sarcoma and needs to be investigated. Other signs include pelvic pain, pressure, and unusual discharge. A nonpregnant uterus that enlarges quickly is suspicious. However, none of the signs are specific. Specific screening test have not been developed; a Pap smear is a screening test for cervical cancer and not designed to detect uterine sarcoma.

GCCs have an aggressive course compared to other appendiceal neuroendocrine tumours.

Carney triad (CT) is characterized by the coexistence of three types of neoplasms, mainly in young women, including gastric gastrointestinal stromal tumor, pulmonary chondroma, and extra-adrenal paraganglioma. The underlying genetic defect remains elusive. CT is distinct from Carney complex, and the Carney-Stratakis syndrome.

GCCs are diagnosed by pathology. They have a characteristic biphasic appearance which includes (1) goblet cell-like cells, and (2) neuroendocrine-type nuclear chromatin (stippled chromatin).

Smooth muscle tumours show a smooth muscle differentiation. There are two main types of smooth muscle tumour: the benign leiomyoma and the malignant leiomyosarcoma.

Some women with uterine fibroids do not have symptoms. Abdominal pain, anemia and increased bleeding can indicate the presence of fibroids. There may also be pain during intercourse, depending on the location of the fibroid. During pregnancy, they may also be the cause of miscarriage, bleeding, premature labor, or interference with the position of the fetus. A uterine fibroid can cause rectal pressure. The abdomen can grow larger mimicking the appearance of pregnancy. Some large fibroids can extend out through the cervix and vagina.

While fibroids are common, they are not a typical cause for infertility, accounting for about 3% of reasons why a woman may not be able to have a child. The majority of women with uterine fibroids will have normal pregnancy outcomes. In cases of intercurrent uterine fibroids in infertility, a fibroid is typically located in a submucosal position and it is thought that this location may interfere with the function of the lining and the ability of the embryo to implant.