Comparison of Akt/mTOR signaling in primary breast tumors and matched distant metastases

The Akt/mammalian target of the rapamycin (mTOR) signaling pathway represents a promising target for cancer therapy. The phosphorylation status of Akt and of mTOR's phosphorylation target eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) is often used to assess the activity of Akt and mTOR signaling. The purpose of this study was to determine whether primary tumors differ from their metastasis in their expression of pAkt and p4E-BP1.

Primary breast tumors and their distant metastases surgically resected from the same patients were evaluated with immunohistochemical analysis (IHC) for pAkt (Ser473) and p4E-BP1 (Ser65). The agreement between the IHC results for the primary tumor and metastases was evaluated with Cohen kappa (kappa).

Most primary breast tumors and metastatic tumors expressed pAkt (76% of each). Of the 23 matched evaluable pairs, however, 11 (47.8%) had discordant IHC results (kappa -0.31; 95% confidence interval [CI], -0.49 to -0.13). Similarly, although most of the primary and metastatic tumors were positive for p4E-BP1 (75% and 74%), of the 23 matched evaluable pairs, 8 (47.8%) were discordant (kappa 0.10; 95% CI, -0.33-0.52).

In this series, most primary breast tumors and metastases expressed pAkt and p4E-BP1 by IHC. Concordance between IHC findings in primary tumors and metastases was poor, however. Further work is needed to determine whether this reflects true biological heterogeneity or poor reproducibility of IHC with phosphospecific antibodies, and to identify which biomarkers can be assessed most reproducibly in primary tumors to predict activity of Akt/mTOR signaling and sensitivity to pathway inhibitors.