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Mucinous breast carcinomas lack PIK3CA and AKT1 mutations

Elizabeth L Kehr1, Julie M Jorns, Daphne Ang

  • 1Department of Pathology, Oregon Health & Science University, Portland, OR 97239, USA.

Human Pathology
|June 19, 2012
PubMed

Insights

Activating PIK3CA mutations are common in invasive breast cancer but absent in invasive mucinous carcinoma. However, these mutations were found in associated ductal carcinoma in situ and hyperplasia, suggesting a role in early breast epithelial proliferation.

Area of Science:

  • Oncology
  • Molecular Biology
  • Genetics

Background:

  • Activating point mutations in phosphatidylinositol-3-kinase catalytic subunit (PIK3CA) are frequent in invasive breast cancer.
  • These mutations are typically found in estrogen receptor-positive and Her2-positive subtypes.
  • The molecular landscape of special morphologic breast cancer types, like mucinous carcinoma, remains less understood.

Purpose of the Study:

  • To investigate the frequency and distribution of PIK3CA mutations in invasive mucinous breast carcinoma.
  • To compare PIK3CA mutation status between invasive mucinous carcinoma and other breast cancer types.
  • To explore the potential role of PIK3CA mutations in associated non-invasive lesions of mucinous breast carcinoma.

Main Methods:

  • Screening of 29 pure invasive mucinous carcinomas and 9 ductal carcinomas with mucinous differentiation for >321 point mutations in 30 genes using multiplex PCR and mass spectrometry.
  • Direct sequencing of PIK3CA hotspot mutations in 3 invasive cases and 25 associated non-invasive lesions (ductal carcinoma in situ, hyperplasia, columnar cell lesions).
  • Comparison with a cohort of invasive ductal carcinomas of no special type.

Main Results:

  • No PIK3CA point mutations were detected in any of the invasive mucinous breast carcinoma samples.
  • This contrasts sharply with the 35% PIK3CA mutation frequency observed in invasive ductal carcinomas of no special type.
  • PIK3CA hotspot mutations were identified in associated ductal carcinoma in situ (3/14) and various hyperplastic lesions (5/11), including atypical ductal hyperplasia, usual ductal hyperplasia, and columnar cell change.

Conclusions:

  • Invasive mucinous breast carcinoma exhibits a unique molecular profile characterized by the absence of PIK3CA mutations.
  • PIK3CA mutations may be involved in the early stages of breast epithelial proliferation, as indicated by their presence in associated non-invasive lesions.
  • These findings support a distinct pathogenetic pathway for invasive mucinous breast carcinoma compared to other invasive breast cancers.

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