MRI: Is it Right for You?

Patient Expert

"Why didn't my doctor order an MRI?"

That's a plaintive question I see repeated on this site over and over again. Many of you whose diagnosis was difficult or prolonged believe an MRI, right up front, would have saved you the time and trouble involved in mammogram callbacks and ultrasounds.

And some of you, having completed treatment and experiencing scary thoughts of "what if it comes back?," are convinced a regular MRI is the best way to identify a recurrence - early, before it turns into metastasis.

And then there are you younger women with small, dense-feeling breasts - in your case, wouldn't an MRI be much more effective at detecting breast cancer than a mammogram?

Magnetic Resonance Imaging (MRI) can be a very effective diagnostic tool. Study data shows it can pick up more cancers, earlier, than mammography (though there are some cancers mammography finds that an MRI can't).

But it's also a much more involved process. A mammogram is a simple X-ray, taking only a minute or so to perform. MRI combines a magnetic field and radio pulses to take multiple pictures of your breast, which are then put together digitally and interpreted by a computer.

Mammograms require nothing more than that you remove your shirt. An MRI requires an injection of contrast dye into your arm, and 30 to 45 minutes of lying face down, perfectly still, in a very tight chamber.

And of course, an MRI is much more expensive than a mammogram; about $4,000, compared to the approx. $125 price tag for a mammogram.

Still, if it's a more sensitive test" isn't it worth the extra bother and expense?

Well, that's the other major issue: MRIs are SO sensitive that they result in a significant number of false positives: areas identified as cancer that aren't. An MRI can mistake breast edema (fluid) for cancer; or it can see a benign fibroadenoma as cancer. Bottom line, it can identify something abnormal in your breast; but it can't tell if it's cancerous. Only a biopsy can do that.

So when is an MRI useful?

First, when it's used for diagnosis, rather than for routine screening. If a mammogram picks up a suspicious area, and an ultrasound doesn't rule it out as a harmless cyst, an MRI will often be used to get a better picture. Since it can determine size and shape more clearly than a mammogram, an MRI can tell your doctor whether the lesion is suspicious enough to warrant a biopsy.

An MRI is also used to determine treatment options after a woman has been diagnosed with breast cancer. It can find tiny additional tumors in the same breast, small enough that they can't be felt, nor seen on a mammogram. It's also invaluable for finding tumors in the other breast. If the "healthy" breast shows nothing suspicious on an MRI, it's pretty certain there's nothing there. This information is key if a patient is trying to decide whether to have a prophylactic double mastectomy.

Still, the number of false positives can be daunting. A recently completed study at Dartmouth-Hitchcock Medical Center in Lebanon, NH, reported in Dartmouth Medicine magazine, examined women with newly diagnosed invasive breast cancer who received followup diagnostic MRIs in the healthy breast. Of the 199 women monitored, 74 (47%) were found to have suspicious lesions in the opposite breast, lesions not picked up by a mammogram.

Of those 74 women, 38 (just over half) were discovered to have cancerous tumors (three-fourths of which were invasive) in their "healthy" breast; while in 36 women, the suspicious lesions were found to be benign, via biopsy.

Second, an MRI is useful when it's used as a screening tool (rather than a diagnostic tool) in certain very specific instances. The American Cancer Society guidelines say that you're a good candidate for MRI screening if you:

-have a BRCA1 or BRCA2 gene mutation;
-have a first-degree relative (parent, sibling, child) with a BRCA1 or BRCA2 mutation;
-have a lifetime risk of breast cancer of 20%-25% or greater, according to your doctor's risk assessment, or a very strong family history;  
-had radiation to the chest between the ages of 10 and 30;
-have Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome, or may have one of these syndromes based on a history in a first-degree relative.

Clearly, the above guidelines include only a small percentage of the population. Thus MRI is seldom used as a routine screening tool - which is why you get a regular screening mammogram, not a regular screening MRI.

There's dispute over one part of the population that might benefit from screening MRIs: women with dense breasts. Evidence has been steadily growing that dense breasts increase your risk of breast cancer, if only slightly. And dense breasts make it harder for a mammogram to pick up tumors or suspicious lesions.

But be aware, dense breasts are a clinical condition; that is, they have to be diagnosed by a radiologist, who'll use something called the BI-RADS scale (Breast Imaging-Reporting and Data System) to determine how dense your breasts are. Officially, you have dense breasts if they're made up of at least 50% fibroglandular tissue that may obscure a tumor.

So just being small-breasted doesn't mean you have dense breasts. Nor does having breasts that feel lumpy or hard. Self-assessment isn't possible; only your medical team can tell you whether or not you have dense breasts.

Bottom line: Women at normal risk for breast cancer don't need screening MRIs; for you, a mammogram is perfect. And women with early breast cancer, cancer whose risk of recurrence after treatment is less than 20%, don't need screening MRIs; even though you fear cancer coming back, a regular mammogram is fine for you, too.

Women with dense breasts? Speak to your doctor. You might decide that the expense and bother of an MRI, combined with your regular screening mammogram, might be worth it.