How Kaposi Sarcoma Is Diagnosed

A definitive diagnosis of Kaposi sarcoma (KS) requires a biopsy and a microscopic evaluation of the tissue sample. However, if your healthcare provider suspects KS, they may order blood tests or imaging first to rule out other possible causes of your symptoms.

Next to lung cancer, Kaposi sarcoma is the second most common cancer seen in people living with HIV in the United States.

This article walks you through how Kaposi sarcoma is diagnosed and what to expect when undergoing a diagnosis.

Self-Checks/At-Home Testing

There are no at-home tests able to check for Kaposi sarcoma. However, KS can often be recognized by the characteristic lesions that can develop on the skin or in the mouth.

KS often starts as flat, discolored patches that rapidly progress into raised purplish, brown, or red bumps, patches, or nodules. The growths can converge into larger patches and may even become cosmetically disfiguring in some people.

KS often develops on the legs or face but can affect any part of the body. The lesions are typically painless, but those on the legs or groin can block the flow of fluid and cause the painful swelling of the legs and feet (known as lymphedema).

KS lesions can also form on mucosal tissues, such as those lining the mouth, nose, eyelids, trachea (windpipe), lungs, and digestive tract. KS lesions are often seen on the gums, in the mouth or throat, on the outside of the eye, or in the inner eyelid. They are typically non-painful and non-itchy.

Although there are several types of KS—including a form that mainly affects older men of Mediterranean or Eastern European descent and another that affects children in Africa—KS is most commonly associated with HIV infection.

Physical Examination

A physical exam is central to the diagnosis of Kaposi sarcoma. Even so, there are challenges in diagnosing the disease, particularly among healthcare providers who are not familiar with KS. Subtle clues can easily be missed, especially in the early stages of the disease.

As part of the evaluation, the healthcare provider will ask you questions about your medical history, including your current symptoms and any past illnesses or infections you may have experienced. You may also be asked if you've been tested for HIV and offered a test if you haven't.

If you have HIV, you will be asked if you're on treatment, what medications you are taking, and if you're having any problems with the treatment.

During the physical exam, the healthcare provider will examine your skin and the inside of your mouth to look for lesions. Because KS lesions can develop in the mucosal tissues of the rectum, the healthcare provider may also recommend a digital rectal exam (in which a gloved finger is inserted into the rectum to check for patches or nodules).

The healthcare provider may also look for signs of KS in the lungs (such as bloody sputum and shortness of breath) or in the digestive tract (such as rectal bleeding and abdominal pain).

If the findings are suggestive of KS, you may be immediately stepped to the next phase of the evaluation, called the biopsy.

Biopsy

Kaposi sarcoma can only be definitively diagnosed with a biopsy and an examination of the tissue samples by a medical pathologist.

A biopsy is a procedure that removes cells or tissues from the body with a knife, needle, or other methods. There are two types commonly used to check for KS:

• Punch biopsy: This involves the removal of a small, tube-shaped piece of skin and tissue using a pencil-like cutting tool with a circular blade.
• Excisional biopsy: This is the removal of an entire lesion with a scalpel. Stitches may be needed to close the wound.

The biopsied tissue is then sent to the lab where the cells are evaluated under a microscope. The pathologist (a physician specializing in diagnosing disease by laboratory analysis) will start by looking for spindle-shaped cells characteristic of all forms of KS.

Because almost all cases of KS are caused by a virus known as the Kaposi sarcoma-associated herpesvirus (KSHV). A LANA stain will be used to test whether the cells have the "footprint" of KSHV.

A positive LANA stain pair with positive microscopic findings can be considered definitive proof of Kaposi sarcoma.

Labs and Tests

There are no blood tests currently available to diagnose Kaposi sarcoma. Although several KSHV blood tests are used for research purposes, none have been submitted to the Food and Drug Administration (FDA) for use in health care settings.

That said, several lab tests may be ordered to assist with clinical decision-making or rule out other possible causes.

Among the tests your healthcare provider may order are:

• CD4 count: This is a blood test used in people with HIV that measures the "strength" of their immune system. It can establish whether a person has AIDS, the most advanced stage of HIV infection, and, in turn, what other investigations should be pursued.
• Viral load: This is a blood test that measures the amount of HIV in a sample of blood. It can help establish whether an HIV treatment is working or needs to be changed.
• Fecal blood occult: This is a test that checks for the presence of blood in the stool. It may help the healthcare provider decide if a more invasive investigation like a colonoscopy is needed.

Imaging

Imaging tests are commonly used in the investigation of Kaposi sarcoma. They can help establish whether the cancer has spread beyond the skin and mouth to the respiratory or digestive tracts.

Although there is no official staging system for KS, the extent to which the tumors have spread factors into the prognosis (the expected outcome) along with your CD4 count and the presence or absence of other systemic (whole-body) illnesses.

Together, these three factors can help predict how long a person with KS will survive and what course of treatment is most appropriate.

Some of the imaging tests used to diagnose KS are radiographic (meaning that they utilize radiation to create images), while others are endoscopic (meaning that a scope is introduced into the body to view internal structures).

Imaging tests commonly used to investigate KS include:

• Chest X-ray: Used to check for KS lesions in the lungs or trachea
• Computed tomography (CT): An imaging tool that composites multiple X-ray images to create three-dimensional "slices" of the chest and abdominal cavity
• Bronchoscopy: A procedure in which a thin, flexible tube with a lighted camera (called a bronchoscope) is fed into the windpipe and lungs to look for lesions in the airways
• Upper endoscopy: A procedure in which a thin, flexible tube with a lighted camera (called an endoscope) is fed into the esophagus, stomach, and small intestine to look for lesions
• Colonoscopy: A procedure in which a thin, flexible tube with a lighted camera (called a colonoscope) is fed into the rectum and colon to look for lesions
• Capsule endoscopy: A procedure in which you swallow a capsule containing a light and tiny camera that captures images as it travels through the digestive tract

During most endoscopic procedures, a special instrument can be fed through the neck of the scope to pinch off a sample of tissue from an internal lesion.

If KS has already been identified on the skin, another sample is usually not needed. This is because the biopsy of an internal lesion may lead to serious bleeding and offers little in the way of additional information.

Differential Diagnoses

It may seem reasonable to assume that the sudden appearance of a raised, purplish lesion in someone with HIV is Kaposi sarcoma. But, the simple fact is that KS mimics many benign (non-cancerous) and malignant (cancerous) conditions and often takes a skilled pathologist to make the correct diagnosis.

Among the conditions your healthcare provider may explore in the differential diagnosis are:

• Acroangiodermatitis: Also known as pseudo-Kaposi sarcoma, acroangiodermatitis is a condition that causes changes in blood vessels due to underlying problems like venous insufficiency (poor blood circulation in the legs) and arteriovenous malformation (an abnormal tangle of blood vessels).
• Angiosarcoma: This is a type of cancer that develops in the lining of blood vessels, including those of the skin and breast.
  
• Hemangioendothelioma: Also known as spindle cell angioma, hemangioendothelioma is a benign tumor that grows inside blood vessels, usually just below the surface of the skin.
• Leiomyoma: This is a benign growth in smooth muscle tissues commonly associated with uterine fibroids that can affect any part of the body, including the skin.
• Pyogenic granuloma: This is a benign tumor in blood vessels that cause smooth, moist skin bumps that tend to bleed easily.
• Stasis dermatitis: This condition is caused by the buildup of fluid in the lower legs due to varicose veins, circulation problems, or heart disease.
• Other sarcomas: Sarcomas are a broad category of cancers affecting bones and soft tissues, including leiomyosarcoma (a cancer of smooth muscles) and fibrosarcoma (a cancer of connective fibrous tissues at the end of bones)
  

Summary

Kaposi sarcoma (KS) is the second most common cancer among people with HIV in the United States, causing red, brown, or purple lesions on the skin or in the mouth, lungs, and digestive tract. It can be diagnosed with a biopsy and a microscopic evaluation of the affected tissues.

Other tests may be performed to determine the extent and severity of the disease, including a CD4 count and imaging studies like a chest X-ray, CT scan, or colonoscopy. These and other findings can predict the likely outcome of the disease and direct the appropriate treatment.

A Word From Verywell

Kaposi sarcoma is not seen as frequently today as it used to be due to the effectiveness of modern antiretroviral therapy. Even so, it is still possible to get KS while you are on treatment and especially if you are not being treated.

To this end, it is important to start antiretroviral therapy if you have been diagnosed with HIV and to remain adherent to treatment so that you can bring your CD4 count up to normal or near-normal levels (ideally 500 or above). The risk of Kaposi sarcoma and many other opportunistic infections can be greatly reduced at this level.