Abstract
Pure mucinous breast carcinoma (PMBC) is characterized by clusters of tumor cells floating in abundant extracellular mucin and can be classified into paucicellular (Type A) and hypercellular (Type B) subtypes. However, the clinicopathological and genomic differences between these two subtypes have not been well characterized. We retrospectively investigated the clinicopathologic features of 45 cases of surgically removed PMBC (31 Type A and 14 Type B). We also performed whole-exome sequencing (WES) in eight cases of PMBC. We found that Type B PMBC occurs at an older age and shows more aggressive clinical behavior than Type A. WES analysis revealed that HYDIN was the most frequently mutated gene in both types of PMBC. Although Type B PMBC showed a tendency toward more frequent genetic alterations, there were no statistically significant differences between the two subtypes in single nucleotide variants or insertions or deletions of bases associated with moderate or high effects. Our results provide additional evidence that PMBCs are clinicopathologically and genetically heterogeneous and lack pathognomonic genetic alterations. Further, Type B PMBC is more frequently associated with lymph node metastasis than Type A.
Highlights
Mucinous breast carcinoma (MBC) is a rare variant of breast cancer accounting for approximately 4% of all breast carcinomas [1, 2]
Among the 45 patients, ductal carcinoma in situ was presented adjacent to Pure mucinous breast carcinoma (PMBC) in 17 cases (37.8%)
LN metastasis occurred in three cases (6.7%), all of which were Type B PMBC
Summary
Mucinous breast carcinoma (MBC) is a rare variant of breast cancer accounting for approximately 4% (range: 1 to 7%) of all breast carcinomas [1, 2]. MBC can be classified into pure and mixed types. Pure MBC (PMBC) is defined as MBC with more than 90% mucinous components, whereas mixed MBC includes more than 50% but less than 90% mucinous components, as well as other types of invasive ductal carcinoma (IDC) [2, 4]. PMBC should be distinguished from mixed MBC because most PMBCs are detected at relatively early stages without lymph node (LN) metastasis, whereas mixed MBCs carry a prognosis similar to IDC [1, 3,4,5]. PMBCs are a heterogeneous group of tumors and can be further classified into two main subtypes by microscopic features of architecture and cytology: the “classical” variant, Type A
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