PEComa (Perivascular Epithelioid Cell Tumor), from the CureRays guide library.

PEComa is a rare family of soft-tissue tumors driven by overactive mTOR signaling; most are benign or borderline and cured by surgery, while the rare malignant ones are now treated with an FDA-approved mTOR-inhibitor drug, nab-sirolimus, alongside surgery and radiation when useful.

What it is.

PEComa stands for 'perivascular epithelioid cell tumor' — a family of rare tumors made of distinctive cells that wrap around small blood vessels and share features of both muscle and pigment cells. PEComas can arise almost anywhere in the body: the uterus, the gastrointestinal tract, the kidney, the lungs, and soft tissues. Most PEComas are benign or of uncertain (borderline) potential and are cured simply by removing them. A minority are malignant and can spread. The most important biological insight is that PEComas are usually driven by loss of the TSC1 or TSC2 genes, which switches on a growth pathway called mTOR — the same pathway involved in the genetic condition tuberous sclerosis, with which some PEComas are associated. This discovery led to a targeted treatment: mTOR-inhibitor drugs that switch the pathway back off. In 2021 the FDA approved nab-sirolimus (Fyarro) specifically for advanced malignant PEComa.

How radiation treats it.

Radiation damages the DNA inside cancer cells so they can no longer divide. For PEComa, surgery is the main treatment for tumors that can be removed, and the targeted drug nab-sirolimus is the key treatment for advanced disease — but radiation has a useful supporting role. It is used after surgery when margins are close or positive, for tumors that can't be safely removed, and to treat painful or growing spots, including a small number of metastases with focused stereotactic radiation (SBRT). Shaped external-beam radiation concentrates the dose on the target while sparing surrounding organs. Because PEComas are rare, radiation is tailored case by case by an expert team. Radiation is painless during delivery, given over one or more sessions depending on the technique, and external-beam treatment leaves no radioactivity in the body.

The ways we can treat it.

External-beam radiation (IMRT). Shaped beams treat the tumor or tumor bed while sparing surrounding organs, useful after surgery with close margins or for tumors that can't be removed.

Stereotactic body radiation (SBRT). Focused high-dose radiation can precisely treat a small number of metastatic spots, for example in the lung, to control limited spread.

Brachytherapy (selected uterine PEComa). For some PEComas of the uterus, radiation sources placed close to the area can deliver a concentrated dose while sparing nearby tissue.

Questions we hear often.

Is PEComa always cancer? No. PEComa is a family of tumors that ranges from benign to malignant. Most are benign or borderline and are cured simply by removing them. Only a minority are truly malignant and able to spread. Pathologists classify each tumor using features like size and cell-division rate to predict how it will behave.

What makes nab-sirolimus work for PEComa? Most PEComas are driven by an overactive growth pathway called mTOR, usually because of loss of the TSC1 or TSC2 genes. Nab-sirolimus blocks mTOR, switching the growth signal back off. Because the drug matches the tumor's biology, it can shrink advanced malignant PEComas — which is why the FDA approved it specifically for this cancer.

Where does radiation fit in? Surgery and, for advanced disease, nab-sirolimus are the mainstays. Radiation plays a supporting role — used after surgery when margins are close or positive, for tumors that can't be removed, or to treat painful or growing spots, including a few metastases with focused SBRT. Your sarcoma team will decide if radiation is helpful in your case.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.