Breast metastases from malignant melanoma with unusual ultrasound features

A 38-year-old woman was referred to our breast unit from a general practitioner with a 2-week history of a palpable 2 cm painless, well-defined, hard, mobile lump in the left breast at 11 o’clock position. No skin changes or axillary lymphadenopathy have been reported. No previous breast examinations.

Digital mammography with tomosynthesis of the left breast revealed bilateral rounded and lobulated, circumscribed, hyperdense masses without calcifications located in the upper inner quadrant of the left breast and in the upper outer quadrant of the right breast.

Ultrasound revealed corresponding to palpation and mammography, a parallel orientated irregular 60mm nodular mass of partially circumscribed and locally indistinct margin, composed of 2 smaller tumors. The nature of the lesion on the ultrasound images is uncharacteristic, of predominantly heterogeneous character with hyperechoic peripheral parts and hypoechoic  (or even anechoic) center and with slight posterior enhancement. Power doppler imaging revealed peripheral and central vascularity and thus ruled out the presence of a central necrosis. The same character of lesion was visualized, in correspondence to a mass seen on the mammogram of the right breast. Surprisingly, ultrasound revealed multiple findings with similar features, suggesting lesions of the same etiology, but different stages of development. No axillary lymphadenopathy was presented on ultrasound.

Metastases to the breast from malignant melanoma [MM] is a rare entity. The incidence of extra-mammary metastatic tumours to the breast is around 2% of all malignant breast tumours [1,2]. However, MM is one of the most common primary tumours to metastasize to the breast [2,3,4,5] and its incidence is increasing worldwide. It should therefore be considered if single, or especially multiple lesions are detected in a patient with history of this malignancy, even 20 years after a primary tumour has been removed [6]. The patient was diagnosed with a cutaneous melanoma of the scapula at the age of 36. Histopathological examination revealed a thickness of 2,8mm, negative resection margins and sentinel node (TNM: T2aN0M0).

Metastatic MM to the breast affects most often premenopausal women with a primary in the trunk and upper limb [7]. Lymphatic or hematogenous spread occur in around 20% of cases [1], any organ could be involved, most commonly liver, lung and brain[1,8]. Clinical features of metastases to the breast are often firm, round masses, located superficial[5,8]. The presence of multiple lesions may suggest diagnosis, however even 75% of cases occur as a solitary mass [2,4] and may have confusing appearances on imaging. On mammograms, they often present features of benign lesions, are well defined, round or lobulated, without spiculations, calcifications or architectural distortion[2,3,5,8,9]. On ultrasound usually, they appear as round, oval or irregular hypoechoic nodules due to necrosis of insufficient vascular supply, however, hypovascularisation can be caused by vessel compression by dense cellular infiltration with poor echo reflectivity of melanin[3,8,10,11,12]. Most lesions of that type are hypoechoic, may be heterogenous- presenting anechoic or hyperechoic areas, frequently associated with posterior enhancement.   In the presented case, ultrasound revealed particularly unusual findings, since hyperechoic breast masses account for only 0,6%-5,6% and only 0,5% of malignant breast lesions[9,10,11,13]. Hiperechogenicity at ultrasound is caused by fatty or fibrous contents, multiple vascular spaces or high cellularity[11,13]. It is important to combine the ultrasound with mammography in case of suspicion of presence of fatty components, which can be excluded by absence of radiolucent areas within the lesion. Masses with indistinct margins, mixed echogenicity and internal vascularity should raise concern for malignancy[11,14]. Hypervascularity and presence of lymphadenopathy are further diagnostic hints for malignancy.

If available, breast MRI may be helpful in differential diagnosis, since melanoma metastases may show high signal on T1 weighted images due to melanin or haemorrhage.

Due to non-discriminatory clinical and radiological findings, diagnosis can be made by detailed history- metastasis to the breast must be considered in any patient with a known malignancy in her/his personal history who presents with a breast mass, histopathological examination and immunohistochemical stains for cytokeratins and melanoma markers (S100, HMB45, Melan-A), which can differentiate MM from a primary breast cancer[2,5]. It is important to inform the pathologist and the clinician about the patients history with this malignancy to avoid unnecessary additional diagnostic procedures. In our case, the diagnosis was made by ultrasound-guided core needle biopsy.

Positron Emission Tomography and MRI of the brain should be performed to assess the metastatic extent of the disease.

PET examination of our patient revealed the disseminated nature of the disease with the metastases in both breasts, right lung, bilateral in adrenal glands, multiple metastases in the subcutaneous tissue, as well as metastases in the lymph nodes of the left axilla, mediastinum and hepatic hilum.

CT scan of brain (the patient has cochlear implants and therefore MRI could not be performed) showed no pathological changes.

Distant metastasis of melanoma is an indicator of poor prognosis with a 5-year overall survival of <20%[15]. Treatment options for MM include surgical resection of isolated metastases, chemotherapy and radiation therapy. The use of targeted therapy and immunotherapy shows improved survival.

Follow-up PET examination performed approximately 3 months after the start of treatment shows significant regression of all metastases.

Written informed patient consent for publication has been obtained.