title: PI3K pathway activation results in low efficacy of both trastuzumab and lapatinib.
abstract: BACKGROUND
  Human epidermal growth factor receptor 2 (HER2) is the most crucial ErbB receptor tyrosine kinase (RTK) family member in HER2-positive (refered to HER2-overexpressing) breast cancer which are dependent on or "addictive" to the Phosphatidylinositol-3-kinase (PI3K) pathway. HER2-related target drugs trastuzumab and lapatinib have been the foundation of treatment of HER2--positive breast cancer. This study was designed to explore the relationship between PI3K pathway activation and the sensitivity to lapatinib in HER2--positive metastatic breast cancer patients pretreated with anthracyclins, taxanes and trastuzumab.
  
  
  METHODS
  Sixty-seven HER2-positive metastatic breast cancer patients were recruited into a global lapatinib Expanded Access Program and 57 patients have primary tumor specimens available for determination of PI3K pathway status. PTEN status was determined by immunohistochemical staining and PIK3CA mutations were detected via PCR sequencing. All patients were treated with lapatinib 1250 mg/day continuously and capecitabine 1000 mg/m2 twice daily on a 2-week-on and 1-week-off schedule until disease progression, death, withdrawal of informed consent, or intolerable toxicity.
  
  
  RESULTS
  PIK3CA mutations and PTEN loss were detected in 12.3% (7/57) and 31.6% (18/57) of the patients, respectively. Twenty-two patients with PI3K pathway activation (defined as PIK3CA mutation and/or PTEN expression loss) had a lower clinical benefit rate (36.4% versus 68.6%, P = 0.017) and a lower overall response rate (9.1% versus 31.4%, P = 0.05), when compared with the 35 patients with no activation. A retrospective analysis of first trastuzumab-containing regimen treatment data showed that PI3K pathway activation correlated with a shorter median progression-free survival (4.5 versus 9.0 months, P = 0.013).
  
  
  CONCLUSIONS
  PIK3CA mutations occur more frequently in elder patients for HER2-positive breast cancer. PIK3CA mutations and PTEN loss are not mutually exclusive. PI3K pathway activation resulting from PTEN loss or PIK3CA mutations may lead to drug resistance to lapatinib and trastuzumab.
authors.affiliation: Department of Medical Oncology, Fudan University Shanghai Cancer Center, Shanghai 200032, China.
authors.forename: Leiping
authors.initials: L
authors.lastname: Wang
authors.forename: Qunling
authors.initials: Q
authors.lastname: Zhang
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Si
authors.initials: S
authors.lastname: Sun
authors.forename: Haiyi
authors.initials: H
authors.lastname: Guo
authors.forename: Zhen
authors.initials: Z
authors.lastname: Jia
authors.forename: Biyun
authors.initials: B
authors.lastname: Wang
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Shao
authors.forename: Zhonghua
authors.initials: Z
authors.lastname: Wang
authors.forename: Xichun
authors.initials: X
authors.lastname: Hu
mesh_terms: D000328:Adult; D000368:Aged; D018943:Anthracyclines / Q000008:administration & dosage; D000903:Antibiotics, Antineoplastic / Q000008:administration & dosage; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics; D000069287:Capecitabine; D058534:Class I Phosphatidylinositol 3-Kinases; D004252:DNA Mutational Analysis; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives; D018572:Disease-Free Survival; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D004789:Enzyme Activation / Q000235:genetics; D005091:Exons / Q000235:genetics; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage / Q000031:analogs & derivatives; D005500:Follow-Up Studies; D018734:Genes, erbB-2; D006801:Humans; D000077341:Lapatinib; D008875:Middle Aged; D009154:Mutation; D009363:Neoplasm Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D051059:PTEN Phosphohydrolase / Q000032:analysis; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000502:physiology*; D011799:Quinazolines / Q000008:administration & dosage / Q000494:pharmacology*; D043823:Taxoids / Q000008:administration & dosage; D000068878:Trastuzumab; D016896:Treatment Outcome
chemical_list: D018943:Anthracyclines; D000903:Antibiotics, Antineoplastic; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D009363:Neoplasm Proteins; D011799:Quinazolines; D043823:Taxoids; D000077341:Lapatinib; D003841:Deoxycytidine; D000069287:Capecitabine; D019869:Phosphatidylinositol 3-Kinases; D058534:Class I Phosphatidylinositol 3-Kinases; C484760:PIK3CA protein, human; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D000068878:Trastuzumab; D005472:Fluorouracil