Mucinous breast carcinoma with neuroendocrine differentiation: Case report

Abstract

Mucinous carcinoma of the breast is rare representing 2% of all breast carcinomas. It can be classified as either a pure or a mixed type. Pure mucinous breast carcinoma has a less aggressive behavior compared with mixed breast mucinous carcinoma. The latter shows frequent neuroendocrine differentiation.

The differential diagnoses of mucinous carcinoma of the breast include mucocele‐like lesions, mucinous cystadenocarcinoma, invasive ductal carcinoma with mucinous features, and invasive lobular carcinoma with extracellular mucin production.

1. CLINICAL IMAGE

An 85‐year‐old woman presented with a slow‐growing tumor in the left breast. Physical examination showed at the upper outer quadrant of the left breast a tumor firm in consistency, without retraction of the surrounding skin. No axillary or supraclavicular lymph nodes were felt. Mammography of the left breast showed a well‐defined high‐density mass with circumscribed margins measuring 55 mm in diameter (Figure 1A,B). Ultrasound‐guided biopsy was performed. Histologically, the tumor was characterized by nests and clusters of cells floating in lakes of mucin partitioned by delicate fibrous septae containing capillary blood vessels (Figure 2A–D). Alcian blue special stain highlighted the extracellular mucin (Figure 3A,B). There was no nuclear atypia, and the mitotic index was low (1 mitosis/10 HPF). The immunohistochemical study showed diffuse and intense positive immunostaining of the tumor cells with chromogranin A (Figure 3C) and synaptophysin (Figure 3D). ER and PgR were diffusely expressed (90% and 100% respectively); the HER2 score was 1+ and Ki67 < 14%. The tumor cells were negative for E‐Cadherin. The diagnosis of mucinous carcinoma of the breast with neuroendocrine differentiation is challenging and relies on histological examination coupled with an immunohistochemical study. ¹ , ² Pathologists should keep in mind the differential diagnoses.

FIGURE 1.

A: Mammography revealing a well‐defined high‐density mass with circumscribed margins measuring 55 mm in diameter (yellow arrow). B: Mammography showing a well‐defined high‐density mass with circumscribed margins measuring 55 mm in diameter (yellow arrow)

FIGURE 2.

A: Core biopsy revealing nests and clusters of cells floating in lakes of mucin partitioned by delicate fibrous septae (Hematoxylin and eosin, magnification × 100). B: Core biopsy showing mucin lakes with some nests of malignant cells set in a background of fibrous stroma. (Hematoxylin and eosin, magnification × 100). C: Nests of tumor cells surrounded by extracellular mucin. The tumor cells were monomorphic with eosinophilic cytoplasm and round or ovoid nuclei with no atypia (Hematoxylin and eosin, magnification × 400). D: Tumor cells were medium‐sized, monomorphic with eosinophilic cytoplasm and round or ovoid nuclei showing stippled chromatin (Hematoxylin and eosin, magnification × 400)

FIGURE 3.

A: Alcian blue special stain highlighting the extracellular mucin (Alcian blue, magnification × 100). B: Alcian blue special stain highlighting the extracellular mucin (Alcian blue, magnification × 400). C: Immunohistochemistry demonstrating strong and diffuse staining of the tumor cells with chromogranin A (brown staining) (Immunohistochemistry, magnification × 100). D: Immunohistochemistry demonstrating strong and diffuse staining of the tumor cells with synaptophysin (brown staining) (Immunohistochemistry, magnification × 400)

2. AUTHOR CONTRIBUTIONS

Dr Faten Limaïem prepared, organized, wrote, and edited all aspects of the manuscript. Dr Faten Limaïem prepared all of the histology figures in the manuscript. Pr Saadia Bouraoui participated in the conception and design of the study, the acquisition of data, analysis, and interpretation of the data. Both authors read, edited, and approved the final version of the manuscript. They contributed equally to preparing the manuscript and participated in the final approval of the manuscript before its submission.

4. CONFLICT OF INTEREST

None declared.

6. ETHICAL APPROVAL

All procedures performed were in accordance with the ethical standards. The examination was made in accordance with the approved principles.

7. CONSENT

Published with written consent of the patient.

Limaiem F, Bouraoui S. Mucinous breast carcinoma with neuroendocrine differentiation: Case report. Clin Case Rep. 2022;10:e06665. doi: 10.1002/ccr3.6665

5.1. DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.