Contemporary Surgery

Which imaging best detects breast cancer?

Department of Surgery Mayo Clinic College of Medicine Rochester, MN

 Department Editor —   David  R.  Farley,  MD

Mayo Clinic College of Medicine, Mayo Graduate School of Medicine, Rochester, MN

  Clinical presentation

Screening mammography in a 42-year-old premenopausal woman detected dense breast tissue and a 7-mm spiculated nodule in the upper-outer quadrant of her right breast (FIGURE 1).

Her family history included a paternal aunt with breast cancer at age 56.

An ultrasound-guided biopsy showed invasive ductal carcinoma, grade 2 (of 3) with extensive ductal carcinoma in situ.

She was referred to the Mayo Clinic for definitive management.

  Surgical consultation

The patient appeared fit and healthy. Physical examination revealed no palpable breast or axillary abnormalities.

She had obtained bilateral magnetic resonance imaging (MRI) of the breast before our consultation. The MRI revealed three lesions in the right breast: a 9-mm rapidly enhancing nodule at the 10 o’clock position that corresponded to the lesion seen on the mammogram; a 3-mm nodule at 12 o’clock; and a 9-mm mass in the retroareolar region (FIGURE 2).

The MRI also revealed two 3-mm enhancing nodules in the central portion of the left breast: posterior to the nipple and at 12 o’clock (FIGURE 3).

Given the MRI evidence of bilateral multiple indeterminate nodules, we reevaluated both breasts with ultrasound. Biopsies at 10, 11 and 12 o’clock positions of the right breast revealed invasive, Nottingham grade 2 (of 3) ductal carcinoma and ductal carcinoma in situ (DCIS). We did not obtain biopsies of the left breast because ultrasound results were negative for malignancy.

After detailed discussions with multiple caregivers (medical oncologist, radiation oncologist, internist, nurse practitioner, and a general surgeon), the patient opted for bilateral skin-sparing mastectomies and right-sided axillary sentinel lymph node biopsy.

Surgery confirms diagnosis

While the left mastectomy specimen was free of malignancy, we identified three separate foci of grade 2 invasive ductal carcinoma in her right breast. The largest tumor measured 0.8×0.7×0.7-cm. Although DCIS was evident, all surgical margins were free of tumor.

The right-sided sentinel node biopsy was positive, and 2 of 20 right axillary lymph nodes were found to harbor estrogen- and progesterone-receptor positive cancer at greater than 10%. The HER2/neu marker was negative.

The patient received six cycles of chemotherapy in the NSABP B-38 study (BOX).¹ She has faired well in follow-up with her local oncologist.

  Problematic screening tools

Diagnostic mammography is recommended for any woman 35 or older who has a breast mass.² Although mammography is the primary study for identifying clinically occult breast cancer, its limits in sensitivity and specificity have led physicians to use other imaging modalities.

Results from eight randomized controlled breast cancer screening trials using mammography with or without clinical breast examination demonstrated a protective effect in women age 50 and older.³ Although far from a perfect screening tool, mammography has resulted in a 20%–30% reduction in breast cancer-related mortality.⁴

Is MRI necessary?

Physicians now use MRI more frequently than before because it can assess and delineate soft breast tissue. While MRI increases the number of abnormalities detected by 27%–36% over mammography,^5,6 it remains inferior to excisional biopsy for in situ cancers and cancers greater than 3 mm.

In patients with clinically suspicious or mammographically identifiable breast lesions, MRI was 88% sensitive but only 67% specific. It had a positive predictive value for malignancy at 72% (mammography 53%).⁷

High-risk patients

High-risk patients have a strong family history of breast cancer and/or known gene mutations. Current research indicates these indications for MRI in high-risk patients (BOX).⁸

• Strong family history of breast cancer. A study of 649 women with strong family histories of breast cancer analyzed the use of both mammography and MRI over 2 to 7 years.

  The study found 35 cancers: 19 by MRI alone, 6 by mammography alone, 8 with both modalities, and 2 interval cases. MRI sensitivity was significantly higher (77%) than mammography (40%, p=0.01). Using both modalities, the sensitivity was 94%. Specificity was 93% for mammography, 81% for MRI, and 77% with both modalities.⁹

• Genetic mutations. A prospective study investigated the use of MRI, ultrasound, mammography, and clinical breast examination for surveillance in 236 women with BRCA-1 and -2 mutations.

  Of the 22 cancers discovered (16 invasive, 6 DCIS), 17 were detected by MRI alone, 8 by mammography alone, 7 by ultrasound alone, and 2 by clinical breast exam. The sensitivity (MRI 77%, mammography 36%, ultrasound 33%, and clinical breast exam 9%) and specificity (MRI 95%, mammography 99%, ultrasound 96%, clinical breast exam 99%) were based on biopsy findings.¹⁰

Expense vs detection rate

MRI is a more sensitive tool for detecting breast cancer than mammography, ultrasound, or clinical breast exam alone,¹⁰ but its specificity remains troublesome.

Should we order hundreds of $1500 tests to find 30% more “abnormalities”, most of which will be benign?

Both of the aforementioned studies^9,10 point out a clinically relevant rationale for using MRI in high-risk patients who are younger, have dense breast tissue, and who have tumors with faster growth rates.

High false-positive rate

Screening mammography, MRI and clinical breast examination were prospectively compared in a cohort of 390 women within a 90-day period.¹¹ Imaging examinations recommended 38 biopsies; 27 were actually performed revealing 4 cancers (MRI detected all 4; mammography found one). Biopsies were recommended in 9% of all MRI studies versus 2% with mammography.

Given the approximately 5% rate of the false-positivity with MRI (leading to benign biopsies),¹¹ is catching a 3-mm cancer via MRI a year before mammography finds the now 5-mm lesion crucial to patient survival? We don’t know.

  Other choices

Ultrasound

Breast ultrasound is a preferable imaging method for evaluation of a clinically symptomatic palpable lump over mammography alone, especially with women who have dense breast tissue, are under age 50, and are at higher risk.

While ultrasound detects mammographically occult cancers about 20% of the time, studies have shown it is not a good screening tool (sensitivity 95%, specificity 69%).¹²

  PET

Similarly, recent studies have not yet found positron emission tomograpy (PET) superior to more traditional imaging modalities in detecting primary breast cancer.¹³ Although PET is advantageous for research, its use for the diagnosis and management of breast cancer is limited.

Our experience

We evaluated the lesions seen on MRI in our patient with ultrasound-guided biopsies in the right breast, confirming cancer. We did not find any worrisome lesions in the left breast using ultrasound.

The outcome of the biopsies allowed us to offer our patient a choice of treatments, and she was able to make an informed decision. Bilateral mastectomies confirmed our diagnosis.

REFERENCES

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