Primary breast lymphoma – multimodality imaging features of a rare entity

A 63-year-old woman was referred to a breast clinic due to 3-month history of a painless palpable breast mass. Patient had a history of surgical excision of benign breast lesions. Clinical examination revealed two nodules in the right breast, with no skin or nipple changes. No axillary lymphadenopathy was detected.

Mammography (Fig. 1a and 1b) revealed two high-density masses in the transition of the inner right quadrants and in the right upper outer quadrant, one with smooth well-circumscribed margins and the other with partially obscured margins. On ultrasound, they appeared as two heterogeneous masses: one round with indistinct margins and posterior acoustic enhancement, non-parallel orientation and showing internal vascularity (Fig. 2a), and the other oval with circumscribed margins, parallel orientation and with no posterior acoustic features (Fig. 2b).

Breast MRI revealed two round and circumscribed masses with an intermediate signal on T2-weighted images (Fig. 3a). The dynamic study (Fig. 3b) revealed a fast heterogeneous enhancement, highlighted in maximum intensity projection images (Fig. 3c), with a predominantly peripheral washout. DWI and ADC map confirmed true diffusion restriction associated with a very low ADC value (Fig. 3d and 3e).

No axillary or internal mammary lymphadenopathy was present.

FDG-PET/CT showed increased FDG uptake of the breast lesions, with no other anomalous uptake sites (Fig. 4).

A core needle biopsy of both lesions was performed, and histopathological results revealed a diffuse large B-cell lymphoma (DLBCL).

Breast lymphoma is a rare hematologic neoplasm with a prevalence of 0.04-0.7%. It can be primary (PBL) or secondary. PBL accounts for less than 1% of breast malignancies and occurs in the absence of previously diagnosed extramammary lymphoma and concurrent widespread disease (except for concurrent ipsilateral axillary and supraclavicular lymph nodes). The most common type of PBL is non-Hodgkin lymphoma, with DLBCL being the most common subtype. The most accepted theory is that PBL arises from intramammary lymph nodes. The median age of patients is 60-65 years (the same age distribution as that of breast adenocarcinoma). Most frequently, PBL is unilateral and right-side predominant. Prognosis depends on the stage and subtype, with DLBCL having the worst prognosis and a higher recurrence rate. The involvement of axillary lymph nodes (stage II) is associated with higher mortality[1].

Imaging features of breast lymphoma are nonspecific and indistinguishable from other breast cancers, and unilateral enlarged lymph nodes, present in advanced stages of this disease, adds no value in the differential diagnosis. At mammography, the most common presentation is a solitary hyperdense mass with a round or oval shape, and circumscribed margins, without calcifications. Infrequent imaging features include asymmetries, skin thickening, and architectural distortion. At the ultrasound, it is depicted as a mass, usually parallel in axis and generally hypervascular. MRI findings usually involve a round or oval mass with mild heterogeneous internal enhancement[2,3]. Dynamic studies can show a slow or rapid enhancement and a plateau in the delayed phase, or, less frequently, a rapid enhancement and washout in the delayed phase[1,3]. The ADC values of lymphoma are markedly lower compared to benign lesions and other malignant lesions due to closely packed lymphocytes with small extracellular spaces, a feature that should raise the possibility of this diagnosis[4].

Final diagnosis requires histopathological results from core biopsy specimens. In our case, a DLBCL not otherwise specified of germinal centre B-cell type was identified.

FDG-PET/CT is recognized as the most accurate technique for staging and treatment response evaluation of FDG-avid lymphomas, such as primary extranodal DLBCL[5]. Treatment most often includes chemotherapy. Surgical excision showed no added benefit in recent studies[6].

A new palpable breast mass can reflect a wide range of pathology from benign lesions as fibroadenoma to malignant lesions such as adenocarcinoma[7]. Given the similar imaging characteristics as breast adenocarcinoma, PBL is hardly suspected with imaging alone, rendering a biopsy essential when suspicious features are present.