No abstract

Background: DCIS is a heterogeneous disease, with increasing incidence. Up to 37% of DCIS overexpress HER2. Lapatinib is a tyrosine kinase inhibitor that directly inhibits HER2 receptor signaling by blocking the receptor's kinase activity. This work tested the hypothesis that Lapatinib inhibits Ras/Raf/MAK and PI3K/AKT signaling in HER2 positive DCIS. Patients and Methods: Patients with HER2 positive (FISH rate >2.2) DCIS diagnosed by core needle biopsy with low risk of having a hidden invasive component were eligible. Neoadjuvant Lapatinib 1500mg daily was administered for 4 weeks prior to surgical resection. EGFR was analyzed by FISH in the biopsy specimen. Ki67, PTEN, AKT, pAKT and pERK were evaluated by IHQ. PI3KCA mutations were screened at exons 9 and 20 by PCR. Apoptosis was analyzed by TUNEL assay. All biological markers were measured before and after Lapatinib treatment. Results: Eleven pts with HER2 positive DCIS have been included to date. Median FISH amplification was 7 (range 2, 70-14). Evaluation pre-Lapatinib showed that: none of the pts had EGFR amplification; six pts (54%) had a Ki67 >25%; pAKT was overexpressed in 3 pts (27%) and pERK in 2 pts (18%); PTEN was deleted in 3 pts (27%). PI3KCA mutations were detected in only 1 pt (9%). After Lapatinib treatment, 9 pts were evaluable. We observed a trend for inactivation of the Ras/Raf/MAK signaling pathway in 7 pts (70%) patients. Interestingly, 3 of these pts had paradoxical activation of PI3K/Akt suggesting a compensatory feed back loop. One out of these 3 pts has PTEN deleted. In addition, 3 pts (33%) showed an increase in the apoptotic index. Conclusions: In our study, four weeks of Lapatinib against HER2 positive DCIS resulted in inactivation of Ras/Raf/MAK pathway; however an activation of the PI3K/Akt was seen as the same time in 3 pts. Nevertheless this trend needs to be confirmed with the inclusion of more pts. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-06-17.