title: Three Metachronous Cases of HER2-Positive Breast Cancer Accompanied with Thyroid Cancer.
abstract: BACKGROUND
  Breast carcinoma (BC) and papillary thyroid carcinoma (PTC) occur predominantly in women. Many studies have shown that PTC is common among women with BC. Collision metastases in lymph nodes do occur but are not common.
  
  
  METHODS
  Here we report 3 metachronous cases of BC with PTC. PTC developed after BC in each case. Histology and immunohistochemistry revealed that HER2 status was positive in each BC, and in 1, concurrent metastases of BC and PTC were shown in a lymph node of the left cervical region.
  
  
  CONCLUSIONS
  From our results, we speculate that women with HER2-positive breast cancer may be at a higher risk for thyroid cancer than other cancers. Finding 2 distinct types of cancer metastasized to 1 lymph node in a patient may, therefore, warrant a high index of suspicion and the use of immunohistochemical stains to differentiate the types of collision tumors.
authors.affiliation: The first Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
authors.forename: Qiqi
authors.initials: Q
authors.lastname: Gao
authors.affiliation: The first Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
authors.forename: Yulong
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: The first Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Wang
authors.affiliation: The first Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
authors.forename: Zihan
authors.initials: Z
authors.lastname: Wu
authors.affiliation: The first Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
authors.forename: Guoping
authors.initials: G
authors.lastname: Ren
keywords: Breast cancer; Collision metastasis; HER2; Immunohistochemistry; Papillary thyroid carcinoma