Expert offers rules for best breast MR practice

Fueled by refinements in practice, advances in research, and explorations of new techniques such as 3T MR spectroscopy, the utility of breast MR is on the rise. Diagnostic Imaging spoke with Dr. Elizabeth Morris, director of breast MRI at Memorial Sloan-Kettering Cancer Center in New York City to obtain an overview of the status and potential of this modality.

DI: Research published in The New England Journal of Medicine last July delivered a validation of breast MR screening of high-risk women. And several papers presented at the 2004 RSNA meeting also reported a high sensitivity for MRI in detecting tumors in patients with a genetic disposition for breast cancer. What is your perspective on using MRI for this purpose?

Morris: Everything that's ever been published shows that in high-risk women, MR is able to pick up cancers not seen on other modalities, particularly mammography. There is compelling evidence that for a small subset of patients who have an elevated risk, MR may be a desirable screening option. But you can define high risk in many different ways.

DI: What is the protocol at MSKCC for high-risk screening with breast MR?

Morris: We performed a trial a few years ago (AJR 2003;181:619-626), and the high-risk patients we included were those with a personal or strong family history of breast cancer, patients with high-risk lesions such as atypia or LCIS (lobular carcinoma in situ), and those treated for Hodgkin's disease. Gene-positive patients made up only about 5% of our study population.

Based on 367 patients in that trial, we had a 4% prevalence of breast cancer on MRI that was not seen on mammography. We also found that in patients with a combined personal history and family history, that number rose to 8%.

So in our patient population, we found pretty compelling evidence that we pick up cancers not otherwise seen. But our indications are broader than those in other studies, which have primarily focused on BRCA1 and BRCA2 patients.

DI: Is there still confusion among referrers and patients about the appropriateness of MR for high-risk screening?

Morris: I think so. And as a result, women are not reimbursed for this test and must pay for it themselves. That's where societies have to take some kind of position. At the RSNA meeting there was talk among several of us that there should be a white paper or recommendations that support screening patients with BRCA1 or BRCA2, for example. Once we get a position paper with a very small, select group of patients, more data can accumulate, and perhaps we can broaden the indications.

But it has to start small. We can't come out and say that all high-risk patients should be screened with MR. That will confuse and overwhelm everyone, and we don't have hard numbers for patients with atypia or LCIS. But we certainly have hard numbers for the BRCA1 and BRCA2 patients, and that is a confined, doable population that can be screened with MR. It's not going to overwhelm the insurance companies or economic resources.

DI: That kind of statement could also help clarify when MR is clearly not appropriate, such as using it for general breast cancer screening.

Morris: When MR first came out, it was positioned as a tool for patients with known cancers and workup of cancers. It's been interesting to see its development as a screening test. Initially, we didn't know that it could pick up small cancers, especially DCIS (ductal carcinoma in situ). As the techniques have gotten better, as the equipment has gotten better, the protocols are much more refined. It has become a much more doable test in a short time period.

DI: What are your thoughts on 3T MRI and how it will advance breast imaging?

Morris: We've done some clinical cases with 3T. The problem is that there is no commercially available coil. We're using an eight-channel coil developed in-house. The image quality to me is comparable to that of 1.5T, but we're not doing matched controlled trials. On the clinical cases that I've done, I can't really tell the 3T images apart from the 1.5T.

I think the benefit of 3T is going to happen with spectroscopy, and that's the reason we're even interested in doing 3T. With 1.5T you can do very good quality imaging, screen, and pick up small cancers. The benefit of 3T is going to be in potentially improving our specificity with MR.

DI: Such as reducing false positives?

Morris: It drives me crazy when people say, "We can't do MR because there are too many false positives." There are no more false positives than with mammography; in fact, there are even fewer if you look at the literature. As far as I'm concerned, we are doing fine with MR. It sure would be nice, however, if we could know in advance if something has a high likelihood of being malignant or not.

Right now, we are just looking at enhancement, enhancement profiles, architecture, and all of those secondary things. It would be so helpful if we had a test that could look at the molecular makeup of these lesions and be able to say, "There's a choline peak there, it's going to be cancer," or "There's no choline peak, so we don't need to stick a needle in it; we could perhaps just watch this."

As a result, we could avoid surgery or MR biopsy for some patients. And you could save a lot in terms of cost, anxiety, and morbidity. There have been some really good data, conducted in Minnesota and at MSKCC by Dr. Lia Bartella, with MR spectroscopy at 1.5T. In her series of 26 patients, there was one false-positive finding with spectroscopy, but there were no false negatives.

DI: If studies are already being done with spectroscopy at 1.5T, what added value will 3T provide?

Morris: The problem with 1.5T is that you have to have fairly large lesions to do spectroscopy. Lesions have to be 1.5 cm, and it's single voxel, and the technique is onerous. It takes about 10 minutes, and someone has to monitor the exam at the scanner.

Three-T MR offers the ability to interrogate small lesions, say 5-mm lesions, and also have a multivoxel setup. Imagine how it would be if you could examine the whole breast with an MR scan and then interrogate it with spectroscopy in five minutes or so and see where the choline peaks are. It is very exciting technology, and it is where things should potentially move in the future.

DI: It's one thing to detect a lesion on MR that is not seen on mammography; it's another to follow up on that finding. What is your protocol for dealing with lesions that appear suspicious on MRI but are not visible on mammography or ultrasound?

Morris: My feeling is, you should not be doing breast MR unless you can put a needle in the lesion. I feel very strongly about that.

DI: An MR-guided needle?

Morris: Absolutely. I get phone calls all the time from surgeons who want to refer patients to me for an MR-guided biopsy. These are patients who underwent an MRI, and the radiologist is recommending a biopsy but is unable to do that biopsy.

When that happens, I will call the radiologist and ask, "Why are you doing this?" They are telling patients that they need a biopsy based on their experience, but in order to build on that experience they need feedback on what they are calling suspicious. And there is no way they are going to know that or get feedback or be able to audit their own practice unless they do their own biopsies.

If you are doing breast MR, you need to know what your positive biopsy rate is. You need to know that areas that you see that show plateau kinetics are often not cancer. This is how you build experience, how you build your eye.

Being able to stick a needle in is an elemental part of a breast MR program. Whether it's a biopsy needle or a localization needle doesn't matter. Obviously, a biopsy needle would be better. But if you are in the business of providing MR, you should be able to buy a $100 needle and put it in the breast so the patient can go to surgery.

DI: What is your preferred technique for MR-guided biopsy?

Morris: We use a vacuum-assisted device. We started with the 14-gauge Truecut, but the specimens were quite small, and there were underestimation issues. For example, at biopsy we would get atypia, but at surgery it would come back DCIS. And it has been very well proven in biopsy literature that with breast disease, the more tissue you get, the better.

So the standard of care these days for breast MR biopsy is vacuum-assisted. You could quibble about what gauge it should be, and there are a few different things on the market, ranging from 11-gauge to an 8-gauge. It doesn't matter so long as you are doing vacuum-assisted.

This is particularly important with MR, because you are seeing such small lesions. You need to be accurate in targeting and in getting the tissue out. Vacuum assistance allows you to accomplish that.

Ms. Dakins is feature editor of Diagnostic Imaging.