Primary breast lymphoma mimicking triple-negative breast cancer: a case report with clinical and pathological implications.

Background: Primary breast lymphoma (PBL) is a rare type of extranodal lymphoma, the diagnostic process for which presents significant challenges owing to an overlap in clinical and pathological features with those observed in triple-negative breast cancer (TNBC). However, the current literature reveals a paucity of information regarding the ramifications of potential diagnostic errors, particularly in the context of emergent therapeutic strategies for TNBC. Thus, we present a unique report of a case of PBL.

Case presentation: A 76-year-old female with no past medical or family history presented to the hospital with the chief complaint of a mass in the right breast. Two masses were palpated in the right breast: one 56 mm mass (No. 1) located at 10 o'clock, and a 21 mm large, elastic, hard mass (No. 2) at 4 o'clock. Needle biopsy was performed only on the larger 56 mm mass (No. 1). The results showed invasive carcinoma that was negative for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2. The preoperative diagnosis was right breast cancer (T3N0M0 Stage IIB) of the TNBC subtype. The patient refused the preoperative chemotherapy recommended by the treatment team; therefore, right breast mastectomy and sentinel lymph-node biopsy were performed instead. The histopathological diagnosis of the first mass was diffuse large B-cell lymphoma (DLBCL); that of the second mass (No. 2) was an invasive breast carcinoma of no special type. Postoperative treatment consisted of endocrine therapy (letrozole) for breast cancer, while the DLBCL was treated with chemotherapy and three courses of intrathecal chemotherapy. At the time of this report, the patient is still living, and neither tumor had recurred in the 2 years following surgery.

Conclusions: On rare occasions, PBL can preoperatively mimic TNBC. While this case did not lead to serious consequences, because surgery was eventually selected as the first therapy, clinicians should be aware that the diagnosis of PBL is challenging using only a core-needle biopsy and can often be misdiagnosed as TNBC.