Review
Metastases to the breast from extramammary malignancies – PET/CT findings☆

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Abstract

Detection of incidental malignant lesions in the breast has a significant clinical impact not only on healthy individuals but also on patients with known malignant disease. This review describes a spectrum of metastatic breast lesions incidentally detected by FDG PET-CT at staging that may be misinterpreted as second primary malignancy. The common non-mammary malignancies that metastasize to the breast include melanoma, hematopoietic malignancies and epithelial cancers. We present the FDG PET-CT features of incidental non-mammary metastases to the breast that may help distinguish primary breast cancer from metastatic disease and aid in the management of patients with a known malignancy.

Introduction

The metabolic information provided by positron emission tomography (PET) using fluorine-18 fluorodeoxyglucose (18F-FDG) has facilitated wide application of this functional imaging modality in the diagnosis and staging of tumors and in the monitoring of response to therapy. PET combined with computed tomography (CT), PET-CT, yields both anatomic and functional data and is an important staging modality for malignancies [1], [2]. FDG-PET, a whole-body imaging modality, has the ability to detect early malignant lesions characterized by an increased rate of glycolysis [2], [3]. FDG-PET has been shown to be more accurate than CT for identifying distant and nodal metastatic disease in a variety of malignancies [4], [5], [6], [7], [8] and also more accurate than CT for identifying recurrence [9], [10]. However, increased FDG uptake has also been described in benign, inflammatory, or infectious processes and in sites of physiologic tracer biodistribution [11], [12], [13]. Unexpected FDG uptake in the breast is increasingly identified by FDG PET-CT secondary to its increased application for cancer staging and follow-up [14]. It is important to characterize the imaging features of these lesions with increased FDG breast uptake in order to determine patient prognosis and management. Chung et al. reported that 163 (0.4%) of 45,000 FDG PET-CT exams exhibited unexpected focal 18F-FDG breast uptake; of which 7 (29%) of 24 biopsy-proven lesions were malignant [15]. The aim of this educational review is to describe metastases to the breast from non-mammary malignancies incidentally discovered at staging FDG PET-CT.

Section snippets

Normal FDG activity in the breast

Normal FDG uptake has been demonstrated in the myocardium, skeletal muscle, and brown fat [11], [13], [16], [17], [18], [19], [20]. Studies have shown that FDG uptake can vary in the normal breast depending on the patient's age, breast density that reflects the amount of glandular tissue, and menopausal status [21], [22]. A correlation has been demonstrated between the intensity of FDG uptake in normal breast tissue and the patient's menstrual cycle. Between the 5th and 15th day of the

Incidental abnormal FDG activity in the breast

FDG PET-CT is useful in the evaluation and management of oncologic patients. When foci of FDG uptake are detected in sites atypical for metastatic spread from the patient's known primary tumor or do not correspond to recognized locations for normal physiologic FDG distribution [24], [25], the distinction between a second primary malignancy, an uncommon focus of metastatic disease, and a benign process (including breast infection, fibroadenoma, or fibrocystic change) should be made. Knowledge of

Imaging characteristics of breast metastases

Several studies have [15], [24], [25] described avid FDG uptake in breast metastases. In our series, the median SUVmax of breast metastasis was 6.8, with a wide range (1.8–37.7), and was frequently similar to the uptake of the primary malignancy. This information should be interpreted with caution, however. Retrospective studies tend to review images in which a breast abnormality is described in the original study report. There is a tendency to describe FDG avid malignant foci and overlook

Metastatic breast disease mimicking primary breast cancer

The morphology of a breast lesion does not always reliably distinguish metastases to the breast from a primary breast cancer, as breast metastases do not always conform to the expected round circumscribed masses described in the literature [23], [24], [25], [26], [27], [28], [30]. Rarely, metastases to the breast may appear irregular and/or may demonstrate associated global trabecular and skin thickening (Fig. 4, Fig. 5), giving the clinical and radiological impression of inflammatory breast

Lymphoma

Of the multiple non-mammary malignancies that metastasize to the breast, lymphoma demonstrates the most variable imaging features. Findings on mammography and sonography can mimic infection, inflammation, and primary breast cancer.

Primary breast lymphoma is defined as malignant lymphoma occurring in the breast in the absence of previously detected lymphoma. The majority of primary breast lymphomas are diffuse large B-cell lymphomas (40–70%). Mucosa-associated-lymphoid-tissue lymphoma of the

Conclusion

We have reviewed the radiologic features of non-mammary malignancy metastatic to the breast, emphasizing the correlation of mammography and ultrasonography with FDG PET-CT imaging. It is important to recognize and correctly diagnose metastasis to the breast, as its prognosis and management differs significantly from that of primary breast cancer. In particular, solitary metastases, needs to be differentiated from primary breast cancer to avoid mutilating surgery. FDG PET-CT does not play a role

Disclaimer

Publication is approved by all authors and explicitly by the responsible authorities where the work was carried out (MD Anderson Cancer Center).

Support

The University of Texas MD Anderson Cancer Center is supported in part by a Cancer Center Support Grant (CA016672) from the National Institutes of Health.

Conflict of interest

The authors have no conflicts of interest.

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    ☆

    An education exhibit on this topic was presented at the 2012 RSNA Annual Meeting, exhibit number: LL-BRE4724.

    1

    Department of Diagnostic Radiology, Unit 1350, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. Tel.: +1 713 745 5149; fax: +1 713 563 9779.

    2

    Department of Diagnostic Radiology, Unit 1478, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. Tel.: +1 713 7452096; fax: +1 713 563 0638.

    3

    Department of Imaging Physics, Unit 1352, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. Tel.: +1 713 563 2711; fax: +1 713 563 8934.

    4

    Unit 0072, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. Tel.: +1 713 745 2535; fax: +1 713 563 9779.

    5

    Department of Diagnostic Radiology, Unit 1478, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. Tel.: +1 713 745 5977; fax: +1 713 563 0638.

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