Kaposi's sarcoma (KS) is a type of cancer that can form masses on the skin, in lymph nodes, in the mouth, or in other organs.

[8] Immunosuppression therapy-related KS generally occurs in people following organ transplantation and mostly affects the skin.

[15] Commonly affected areas include the lower limbs, back, face, mouth, and genitalia.

[19] Lesions in the mouth may be easily damaged by chewing and bleed or develop secondary infection, and even interfere with eating or speaking.

The gastrointestinal lesions may be silent or cause weight loss, pain, nausea/vomiting, diarrhea, bleeding (either vomiting blood or passing it with bowel movements), malabsorption, or intestinal obstruction.

[22] KSHV encodes oncogenes, microRNAs and circular RNAs that promote cancer cell proliferation and escape from the immune system.

Higher rates of transmission among gay and bisexual men have been attributed to "deep kissing" sexual partners with KSHV.

Prudent advice is to use commercial lubricants when needed and avoid deep kissing with partners with KSHV infection or whose status is unknown.

[citation needed] Despite its name, in general it is not considered a true sarcoma,[27][28] which is a tumor arising from mesenchymal tissue.

[29] KS may arise as a cancer of lymphatic endothelium[30] and forms vascular channels that fill with blood cells, giving the tumor its characteristic bruise-like appearance.

[citation needed] Although KS may be suspected from the appearance of lesions and the patient's risk factors, a definite diagnosis can be made only by biopsy and microscopic examination.

[citation needed] In differential diagnosis, arteriovenous malformations, pyogenic granuloma and other vascular proliferations can be microscopically confused with KS.

Since Moritz Kaposi first described the cancer, the disease has been reported in five separate clinical settings, with different presentations, epidemiology, and prognoses.

However, in a certain percentage[vague] of such people, Kaposi sarcoma may recur after many years on HAART, especially if HIV is not completely suppressed.

[50] Limited basic and clinical evidence suggest that topical beta-blockers, such as timolol, may induce regression of localized lesions in classic as well as HIV-associated Kaposi sarcoma.

Kaposi sarcoma entered the awareness of the general public with the release of the film Philadelphia, in which the main character was fired after his employers found out he was HIV-positive due to visible lesions.

In people with AIDS, Kaposi sarcoma is considered an opportunistic infection, a disease that can gain a foothold in the body because the immune system has been weakened.