Barely Benign

From OncoLog, April 2008, Vol. 53, No. 4

Barely Benign

by Sunni Hosemann

Most benign tumors are rather harmless. By definition, they lack the ability to metastasize, and many don’t even spread significantly in terms of the space they occupy. Moreover, they are often located in places where they do no damage to neighboring organs or surrounding structures.

But when benign tumors are growing inside the unforgiving confines of the skull, on or near delicate brain tissues, vital vessels, and major nerves, they can do considerable harm. They can even kill. And in these cases, benign tumors must be dealt with to prevent death and disability.

That’s why specialists at M. D. Anderson treat just as many, if not more, benign intracranial tumors as malignant brain growths. As many as one-third of all brain tumors are benign, said Franco DeMonte, M.D., a professor in and deputy chair of M. D. Anderson’s Department of Neurosurgery, though he treats an even higher percentage since benign tumors are more common in the skull base (his specialty) than other regions of the brain. “Easily half—perhaps two-thirds—of the patients I treat have benign tumors,” said Dr. DeMonte, who also serves as medical director of the institution’s Brain and Spine Center and co-director of the Skull Base Tumor Program.

The benign brain growths most commonly seen include meningiomas, schwannomas, craniopharyngiomas, and pituitary tumors. Rarer benign intracranial lesions include glomus tumors, choroid plexus papillomas, and hemangioblastomas, all of which are highly vascularized; epidermoid and dermoid cysts, which arise from cutaneous epithelial cells displaced during embryonic development; and a variety of others.

Some of these tumors are discovered incidentally by imaging done for unrelated reasons, which is a relatively common occurrence given the widespread use of magnetic resonance imaging (MRI), Dr. DeMonte said. Other times, patients present with significant symptoms, such as headaches, loss of vision, seizures, or balance problems. Occasionally, deficits accumulate so slowly that a tumor may not be suspected as the cause; for example, gradual hearing loss due to a tumor can become profound but often is attributed to other causes or accepted as part of aging. The same can be true of mental functions that have declined slowly over time and gradual personality changes.

Imaging alone is usually sufficient to determine that a mass is benign—that it is not a primary or metastatic cancer—and very often imaging is also sufficient to diagnose the tumor type. “MRI is the most important imaging tool in this regard, as its high sensitivity makes it the gold standard for detecting and delineating even very small masses,” Dr. DeMonte said. “But computed tomography (CT) scanning plays a very important role as well, because it is superior in showing bony involvement, and that can be an important factor in assessing some intracranial tumors.” Being able to assess bony involvement is important because lesions can slowly erode bony portions of the skull over time. A smooth erosion is seen with benign tumors, whereas actual bone destruction is often seen with malignant tumors. In addition, some tumors, mainly meningiomas, can cause excess bone growth, and some tumors become calcified; these are best evaluated with CT as well.

A conversation begins

When a patient is diagnosed with a cancer, the discussion between the physician and patient usually centers on various options for treatment. It will likely be about removing the tumor, deciding when, and perhaps explaining how, that will be done, and discussing whether other treatment modalities such as radiation or chemotherapy will be used.

When a tumor is benign, however, the conversation is often about whether to remove it surgically, treat it with radiation, or simply keep a close watch over it. This sort of discussion is therefore more involved, according to Paul Gidley, M.D., an associate professor in M. D. Anderson’s Department of Head and Neck Surgery. Dr. Gidley is a neuro-otologist who brings his unique specialty to bear in the surgical treatment of skull base tumors and tumors that involve the temporal bone and lateral skull base.

“First, we must do no harm,” he said of the approach to treating benign tumors. “It does not benefit the patient to treat a benign tumor and leave the patient with more problems than were present at the outset.” Thus, the post-diagnosis assessment becomes all-important for these kinds of tumors. This assessment includes a comprehensive history and physical examination, imaging studies, and often, tests to evaluate existing deficits (in hearing, for example).

The size and location of a tumor, its aggressiveness and damage potential, and the symptoms or deficits it is already causing are all important factors that must be weighed against the risk of intervention. A tumor growing inside the confined space that houses the carotid artery or jugular vein, for example, can be life-threatening and should be removed. If a tumor is not threatening vital processes or is causing minimal symptoms or if the risk of complications from treatment is high, the discussion may focus on monitoring it over time.

“I tend to make a tumor prove that it needs treatment,” Dr. DeMonte said. “And therefore, if the tumor is not growing and not causing symptoms, I’m able to tell patients they don’t need surgery or other therapy. I have patients that we’ve been watching for 15 years.”

But patient preference is also an important factor. Some patients are very averse to the idea of leaving a tumor in place, even when its effects are minimal. Conversely, even when it’s medically evident that a tumor should be treated, some patients have strong biases against surgery and radiation therapy. So, these discussions are very specific and individualized. They are a process—a series of conversations—rather than a simple, one-stop consultation.

Treatment options

Surgery

When a tumor has proven that it needs treatment—when the risks of the growth outweigh the risks of intervention—the first option to consider is usually surgery. “Preserving and optimizing function is the most important factor when we’re talking about benign tumors, which often lie on or perilously close to major nerves,” Dr. Gidley said. He performs microscopic surgery for these kinds of lesions, using a variety of devices to monitor nerve function as he removes tumor tissue incrementally. Electrodes can be strategically placed on the face to show facial nerve responses. A device can be placed in the larynx to monitor vocal cord function, and hearing can be monitored with an instrument that generates sound in the ear and causes a brainstem response.

These techniques, along with surgeon experience, enhance the safety of these procedures and thus change the risk-benefit equation. Ancillary rehabilitative services available at M. D. Anderson can also help patients who present with significant nerve deficits caused by these tumors. These can include audiology services; speech, language, and swallowing therapies; neuropsychology and behavioral psychology services; nutrition services; and occupational and physical therapy.

Radiation therapy

For some patients, radiation therapy is a better option than surgery. “A few days ago, I saw two patients who have similar tumors,” Dr. DeMonte said. “One of them is a healthy 38-year-old man, and the other is in his late 50s and represents a higher risk: he’s had bypass surgery and is on aspirin and clopidogrel, an anti-platelet drug. For the higher-risk patient, radiation therapy provides an alternative to surgery. Occasionally, this is also a patient preference.”

Anita Mahajan, M.D., an associate professor in radiation oncology, specializes in radiation treatments and radiosurgery for intracranial tumors. Radiosurgery refers broadly to the use of highly focused radiation beams in a single session. The beams can be shaped and are precisely aimed using computer-calculated, stereotactic, three-dimensional coordinates to destroy tumor tissue with minimal risk to surrounding healthy tissue. Fractionated radiation therapy, given in daily sessions over several weeks, can be delivered with a technique known as three-dimensional conformal radiation, which also uses multiple customized beams. Intensity-modulated radiation therapy (IMRT) allows alteration of the beam intensities coming from different directions to produce a truly customized dose.

The radiation oncologist has an array of tools to choose from to treat a given tumor; at M. D. Anderson, linear accelerator–based (photon) and particle beam–based (proton) systems are available. The decisions about which tool to use and whether to deliver treatment in one session or fractionated over a period of days or weeks are based on factors specific to the individual patient. For example, some techniques are better suited to certain tumor shapes than others: IMRT is better suited to treat an irregularly shaped tumor than are other modalities, including proton therapy, which is considered when minimal irradiation of surrounding tissues is crucial—in children, for example.

In all cases, patient factors that might be considered “practical” are an important part of the decision as well. For example, some radiation techniques require patients to be able to tolerate certain positioning requirements, and that may not be feasible for some people.

Not least in the list of considerations is the patient’s ability to visit the facility for treatments, and in some cases, this can affect a decision about whether to deliver the radiation in one session or over a period of 2 to 6 weeks. The latter is generally preferable, as a larger dose can be given over time with less risk to normal tissues.

Radiation therapy is sometimes used as an adjuvant to surgery for intracranial tumors. Because of the incredible density of vital neurovascular structures at the base of the skull, surgeons sometimes must stop short of complete resection of benign tumors to avoid damaging delicate and critical structures. Radiation therapy can be used to control residual tumor if it continues to grow or cause symptoms. For example, hormone hypersecretion, which occasionally continues after incomplete removal of some pituitary tumors, can be treated in this way.

Combined therapy

In some cases, the best treatment is a planned combination of surgery and radiation therapy, Dr. Mahajan said. That approach would be used for a patient with a very large meningioma at the skull base or a cavernous sinus meningioma, for instance. In such situations, the surgeon removes the part of the tumor that is compressing the optic nerves or brainstem, and radiation treatments follow to achieve control of the rest. The surgery relieves compression by reducing the bulk of the tumor, and the radiation treats the remainder of the lesion. This approach achieves good results in terms of eradicating the maximum amount of tumor while minimizing risk.

“These tumors are challenging because there are so many options for treatment, and so many patient variables,” said Dr. Mahajan, who, like her surgical colleagues, finds that the physician-patient discussion must include an exploration of various patient constraints, needs, and desires to choose the optimal treatment for an individual patient. Above all, she agrees that benign tumors—unlike their cancerous counterparts—must prove that they can be treated without the patient losing functional ground.

For more information, call Dr. DeMonte at 713-563-8705, Dr. Gidley at 713-745-5146, or Dr. Mahajan at 713-563-2350.

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