Rhabdomyosarcoma: a cancer that develops from mesenchymal cells

Description

When mesenchymal cells fail to fully differentiate into skeletal muscle myocytes, they become Rhabdomyosarcoma (RMS), a very aggressive kind of cancer. Rhabdomyoblasts are recognised as malignancy cells. There are four subtypes: Spindle cell/sclerosing rhabdomyosarcoma, alveolar rhabdomyosarcoma, and pleomorphic rhabdomyosarcoma. The two primary forms of soft tissue sarcomas are embryonal and alveolar, and these are the most prevalent in childhood and adolescence. In adults, the pleomorphic form is typically encountered.

Given that children under the age of 18 account for the vast majority of cases, it is typically thought of as a childhood disease. Due to how it appears on an H&E stain, it is frequently referred to as one of the small-blue-round-cell tumours of children. Despite being very uncommon, it makes up around 40% of all soft tissue sarcomas that have been documented.

Any soft tissue region in the body can experience RMS, although the head, neck, orbit, genitourinary tract, genitals, and extremities are where it most commonly manifests. Although there are certain congenital defects connected with the condition, there are no obvious risk factors. The prognosis is highly related to the location of the main tumour, and the signs and symptoms vary depending on the position of the tumour. Lungs, bone marrow, and bones are typical locations for metastasis. RMS can be categorised using a wide range of established histological classifications. About 60% of instances of rhabdomyosarcoma are of the most frequent kind, embryonic.

Definitive classification of subtypes has been challenging because to the challenge in diagnosing rhabdomyosarcoma. As a result, classification schemes differ depending on the institute or company. However, there are four histological subtypes of rhabdomyosarcoma mentioned in the 2020 WHO classification: spindle cell/sclerosing, pleomorphic, alveolar, and embryonal.

The most prevalent histological form, including perhaps 60%–70% of childhood cases, is Embryonal Rhabdomyosarcoma (ERMS). With a maximum documented incidence of 4 cases per 1 million children, children 0 to 4 years old are the age group when it is most prevalent. Spindle-shaped cells with a stromal-rich appearance are the defining feature of ERMS, and their morphology is comparable to that of the growing muscle cells in a 6 to 8 week-old embryo. Both the genitourinary tract and the head and neck frequently have tumours. Almost always, mucosal-lined organs including the vagina, bladder, and nasopharynx are home to botryoid rhabdomyosarcoma (although presentation in the nasopharynx typically affects older children). It frequently appears as a spherical, grape-like lump on the damaged organ in infants younger than a year old. Histologically, the epithelium-covered thick tumour layer that defines the botryoid variants cells (cambium layer). The outlook is favourable for this subtype. The second most typical kind is Alveolar Rhabdomyosarcoma (ARMS). Approximately 20%-25% of RMS-related tumours are ARMS, and it affects persons of all ages equally, with a frequency of one case per million individuals aged 0 to 19. Due to their susceptibility to the embryonal variety, young adults and teenagers are where this form of RMS is most frequently found. Although there have been varieties found without these distinctive alveolar spacings, this form of RMS is defined by tightly packed, spherical cells that cluster around spaces that resemble pulmonary alveoli.

The extremities, trunk, and peritoneum are where ARMS tends to develop more frequently. It frequently exhibits greater aggression than ERMS. Pleomorphic rhabdomyosarcoma, also known as anaplastic rhabdomyosarcoma, is characterised by the presence of large, lobate hyperchromatic nuclei and multipolar mitotic patterns in the cells. High heterogeneity and extremely poor differentiation can be seen in these tumours. Pleomorphic cells can be confined or widespread, with the latter variation being associated with a worse prognosis. It usually affects adults, seldom affects kids, and is frequently found in the extremities.