J Pathol Transl Med.  2020 Jan;54(1):95-102. 10.4132/jptm.2019.10.24.

Clinicopathologic characteristics of HER2-positive pure mucinous carcinoma of the breast

Affiliations
  • 1Department of Pathology and Translational Genomics, Samsung Medical Center, Sungkyunkwan University College of Medicine, Seoul, Korea
  • 22Division of Breast and Endocrine Surgery, Specialized Surgical Unit, King Abdullah Medical City, Makkah, Saudi Arabia
  • 3Division of Breast Surgery, Department of Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
  • 4Division of Hematology-Oncology, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

Abstract

Background
Pure mucinous carcinoma (PMC) is a rare type of breast cancer, estimated to represent 2% of invasive breast cancer. PMC is typically positive for estrogen receptors (ER) and progesterone receptors (PR) and negative for human epidermal growth factor receptor 2 (HER2). The clinicopathologic characteristics of HER2-positive PMC have not been investigated.
Methods
Pathology archives were searched for PMC diagnosed from January 1999 to April 2018. Clinicopathologic data and microscopic findings were reviewed and compared between HER2-positive PMC and HER2-negative PMC. We also analyzed the differences in disease-free survival (DFS) and overall survival according to clinicopathologic parameters including HER2 status in overall PMC cases.
Results
There were 21 HER2-positive cases (4.8%) in 438 PMCs. The average tumor size of HER2-positive PMC was 32.21 mm (± 26.55). Lymph node metastasis was present in seven cases. Compared to HER2-negative PMC, HER2-positive PMC presented with a more advanced T category (p < .001), more frequent lymph node metastasis (p = .009), and a higher nuclear and histologic grade (p < .001). Microscopically, signet ring cells were frequently observed in HER2-positive PMC (p < .001), whereas a micropapillary pattern was more frequent in HER2-negative PMC (p = .012). HER2-positive PMC was more frequently negative for ER (33.3% vs. 1.2%) and PR (28.6% vs. 7.2%) than HER2-negative PMC and showed a high Ki-67 labeling index. During follow-up, distant metastasis and recurrence developed in three HER2-positive PMC patients. Multivariate analysis revealed that only HER2-positivity and lymph node status were significantly associated with DFS.
Conclusions
Our results suggest that HER2-positive PMC is a more aggressive subgroup of PMC. HER2 positivity should be considered for adequate management of PMC.

Keyword

Breast neoplasms; Receptor, ErbB-2; Pure mucinous adenocarcinoma
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