The incidence of bilateral breast cancer is reported as 0.3% to 12% of all breast cancers [1], with the value for synchronous bilateral carcinoma of the breast (SBC) reported as 1.0% and metachronous bilateral carcinoma (MBC) of the breast as 7% of all breast cancers [2].

Apocrine breast cancer is a rare disease reportedly accounting for 0.3% to 1% of all breast cancers [3], and metachronous bilateral noninvasive breast cancer is even rarer and has not been reported to date. A case of bilateral noninvasive breast cancer with unilateral metachronous apocrine breast cancer, an extremely rare case, diagnosed by preoperative CNB is reported.

The patient was a 73-year-old woman with a history of atrial fibrillation and hypertension after surgical treatment of uterine fibroids. She underwent right mastectomy and sentinel lymph node biopsy for right breast cancer five years ago. The histopathological results were as follows: ductal carcinoma in situ (papillary ductal carcinoma), pTis (8.3 × 4.3 cm), pN0 (sn 0/3), M0, pStage 0, ER 10%, PgR 0%, HER2 3+, Ki67 20%, and HG2. After the subsequent five years without postoperative follow-up visits, she noticed a lump in her left breast a week ago and visited the author’s clinic again. On palpation, an elastic, hard mass approximately the size of 3.8-centimeter was palpable in the upper-outer quadrant and in the upper-inner quadrant of the left breast. No enlarged axillary or supraclavicular lymph nodes were observed.

Mammography (MMG) revealed an irregular mass shadow measuring approximately 3.8 cm in the left M-O region of the breast (Figure 1A and Figure 1B).

Ultrasonography (US) revealed an irregular mass shadow measuring approximately measuring approximately the size of 3.8 cm in the upper-outer quadrant and in the upper-inner quadrant of the left breast. Color Doppler echo imaging showed a hypervascular pattern (Figure 2A and Figure 2B).

Core needle biopsy (CNB) was performed (Figure 2C and Figure 2D). The results demonstrated apocrine breast cancer.

Tumor cells were polygonal with densely stained nuclei and eosinophilic, granular, or vacuole-rich cytoplasm, proliferating in a solid manner and partly forming a ductal structure. Nuclear anisokaryosis was observed. These findings demonstrated DCIS with tumor cells showing apocrine features (Figure 3A and Figure 3B).

Computed tomography (CT) revealed an irregular area in the upper-outer quadrant and in the upper-inner quadrant of the left breast under contrast enhancement (Figure 4A and Figure 4B).

Magnetic resonance imaging (MRI) revealed non-mass enhancement in the upper-outer quadrant and in the upper-inner quadrant of the left breast (Figure 5).

The treatment plan was determined at a preoperative multidisciplinary conference attended by breast surgeons, radiologists, and pathologists.

Based on imaging tests such as MRI, the tumor was found to be 3.8 cm in size and had spread close to the nipple; therefore, a partial mastectomy was not an option, and a total mastectomy was selected. Although the preoperative CNB indicated noninvasive cancer, it is only after examining all sections of the postoperative specimen that it becomes clear whether the tumor consists entirely of noninvasive carcinoma and contains no invasive carcinoma. For this reason, it is desirable to combine this approach with sentinel lymph node biopsy to minimize the burden on the patient as much as possible.

Right mastectomy and sentinel lymph node biopsy were performed. The histopathological results were as follows: pStage 0 (TisN0M0), apocrine ductal carcinoma in situ (38 × 18 × 33 mm), high nuclear grade, margin-,pN0 (sn 0/4), ER−, PgR−, AR (androgen receptor) 80%, HER2−, and Ki67 5–10%.

The treatment plan for postoperative adjuvant therapy involved no adjuvant therapy because it was noninvasive cancer.

Follow-up observations two years after surgery show no signs of recurrence.

The incidence of bilateral breast cancer is reported as 0.3% to 12% of all breast cancers [1], with the value for SBC reported as 1.0% and MBC as 7% of all breast cancers [2],[3].

Bilateral noninvasive breast cancer with metachronous apocrine breast cancer is extremely rare and has not been reported to date. Apocrine breast cancer is a rare disease reportedly accounting for 0.3% to 1% of all breast cancers [4]. The mean age of patients is 57.0 years, which is slightly higher than that of ordinary breast cancer.

Apocrine carcinoma of the breast is defined as a special histologic subtype of invasive carcinoma with dominant apocrine metaplasia. The WHO’s essential and desirable criteria define it as a tumor that exhibits apocrine morphology in more than 90% of tumor.

Clinically, apocrine carcinoma usually presents with a palpable tumor mass, rarely with a bloody discharge from the nipple or as a cyst [5],[6].

Histologically, apocrine carcinoma of the breast exhibits a ductal structure and is characterized by eosinophilic, granule-rich cytoplasm. Compared with benign apocrine metaplasia, apocrine carcinoma of the breast is characterized by larger nucleoli and more marked anisocytosis. This is a rare disease reportedly accounting for 0.3% to 1% of all breast cancers.

Apocrine carcinoma of the breast has no characteristic imaging findings compared with ordinary breast cancer. Most cases of ordinary noninvasive breast cancer are luminal type, while many cases of noninvasive apocrine carcinoma of the breast have the phenotype ER−, PgR−, and AR+ [7]. The positivity rate of HER2 is 30–60% [8],[9]. The risk of recurrence increases in cases with HER2 positivity [10] and high Ki67 [11]. Regarding prognosis, there is no difference in survival or recurrence rates compared with ordinary ductal carcinoma [12].

Apocrine breast cancer is a rare disease, and bilateral noninvasive breast cancer with metachronous apocrine breast cancer is even rarer and has not been reported to date. An extremely rare case of noninvasive apocrine carcinoma of the breast—namely, metachronous bilateral noninvasive breast cancer with unilateral rare apocrine breast cancer diagnosed by preoperative CNB—was reported.