Adenomyoepithelioma with a human epidermal growth factor receptor 2-fluorescence in situ hybridization-confirmed ductal carcinoma in situ component: A case report and review of the literature

Abstract

Introduction: Breast adenomyoepithelioma (AME) is a rare tumor composed of myoepithelial cells and ductal or luminal cells. Most cases of AME are benign, but rare cases in which either or both cell types exhibited malignant features have been reported. Due to its rarity, no diagnostic criteria for malignancy have been established for AME.

Patient concerns: A 64-year-old woman presented with a mass in her right breast. Fine-needle aspiration cytology and biopsy examinations revealed lesions composed of spindle-shaped cells and round epithelial cells. AME was suspected, and partial mastectomy was performed.

Diagnosis: The tumor specimen showed AME, which mainly consisted of spindle-shaped myoepithelial cells with slight atypia, admixed with tubular luminal cells and small areas of atypical intraductal proliferative lesions. No apparent features of malignancy, such as necrosis or invasion, were seen in the myoepithelial cells or the luminal or intraductal component. However, the atypical intraductal component exhibited focal nuclear atypia, a cribriform pattern, and moderate to strong membranous human epidermal growth factor receptor 2 (HER2) immunoreactivity. HER2 amplification was detected in focal regions of the atypical intraductal component by fluorescence in situ hybridization (FISH), which resulted in a diagnosis of AME with ductal carcinoma in situ.

Outcomes: The patient did not receive further therapy and was free from tumor recurrence at 23 months after the operation.

Conclusion: HER2 FISH might be useful for evaluating suspected AME tumors for malignancy when an atypical ductal lesion that lacks definitive features of malignancy is encountered.

Figure 1

MRI findings. The horizontal view showed a nodular lesion (arrow), which measured 30 × 30 mm. MRI = magnetic resonance imaging.

Figure 2

Cytological findings. (A) A large and nodular cell cluster was found within the background of myoepithelial cells. (B) Slightly atypical spindle-shaped or round cells with occasional intranuclear inclusion bodies were seen (inset arrowhead). Bar A: 100 μm, B: 20 μm.

Figure 3

Lumpectomy findings. (A) A gross view of the tumor showed a well-defined, firm, whitish multinodular lesion. (B) A whole histological section of the tumor showed that it consisted of a spindle cell lesion (square), a tubular epithelial lesion (circle), and an intraductal component (arrowhead). (C) The spindle-shaped tumor cells only exhibited slight nuclear atypia. (D) The tumor cells in the tubular epithelial lesion also only showed slight nuclear atypia. (E) The intraductal lesion demonstrated a papillary or cribriform growth pattern. The tumor cells of the intraductal lesion displayed increased nuclear atypia. Bar B, 2.5 mm; C and D, 100 μm; E, 250 μm.

Figure 4

Immunohistochemical findings. The spindle cell component was positive for AE1/AE3 (A), focally positive for SMA (B), and negative for the ER (C). The tubular luminal lesion was positive for AE1/AE3 (D), negative for SMA (only the outer myoepithelial cells were positive for SMA) (E), and negative for the ER (F). The intraductal component was positive for AE1/AE3 (G), negative for SMA (only the outer myoepithelial cells of the intraductal component were positive for SMA) (H), and negative for ER (I). Bar A–F: 100 μm, G–I: 250 μm. ER = estrogen receptor; SMA = smooth muscle actin.

Figure 5

HER2 immunohistochemistry and HER2 FISH. (A) HER2 immunoreactivity varied from equivocal (area 1) to positive (area 2) in the tubular lesion and atypical intraductal proliferative lesion, respectively. HER2 FISH showed no amplification (HER2/CEP17: 1.48) in area 1 (B), but clear amplification (HER2/CEP17: 6.0) in area 2 (C). Bar A: 250 μm. CEP = chromosome enumeration probes, FISH = fluorescence in situ hybridization, HER = human epidermal growth factor receptor.