No abstract

HER2 mutations defi ne a subset of metastatic breast cancers with a unique mechanism of oncogenic addiction to HER2 signaling. We explored activity of the irreversi ble pan-HER kinase inhibitor neratinib, alone or with fulvestrant, in 81 patients with HER2mutant metastatic breast cancer. Overall response rate was similar with or without estrogen receptor (ER) blockade. By comparison, progression-free survival and duration of response appeared longer in ER + patients receiving combination therapy, although the study was not designed for direct comparison. Preexistent concurrent activating HER2 or HER3 alterations were associated with poor treatment outcome. Similarly, acquisition of multiple HER2 -activating events , as well as gatekeeper alterations, were observed at disease progression in a high proportion of patients deriving clinical benefi t from neratinib. Collectively, these data defi ne HER2 mutations as a therapeutic target in breast cancer and suggest that coexistence of additional HER signaling alterations may promote both de novo and acquired resistance to neratinib. SIGNIFICANCE: HER2 mutations defi ne a targetable breast cancer subset, although sensitivity to irreversible HER kinase inhibition appears to be modifi ed by the presence of concurrent activating genomic events in the pathway. These fi ndings have implications for potential future combinatorial approaches and broader therapeutic development for this genomically defi ned subset of breast cancer.

Purpose: It has previously been reported that the patient response to gefitinib depends on the presence of mutations within the kinase domain of epidermal growth factor receptor (EGFR) or the expression of its truncated form, EGFR variant III (EGFRvIII). The focus of this study was to determine if these alterations are present within the tyrosine kinase and ligand-binding domain of EGFR in urothelial carcinoma. Experimental Design: The kinase domain found within exons 18 to 21 of the EGFR from 11 bladder cancer cell lines and 75 patient tumors were subjected to automated sequencing. EGFRvIII expression was determined by immunohistochemistry using a urothelial carcinoma tissue microarray, and its expression was subsequently verified by reverse transcription PCR, real-time PCR, and Western blot analysis, using an EGFRvIII-transfected glioblastoma cell line and glioblastoma tumors as positive controls. Results: Our analysis failed to detect mutations within the tyrosine kinase domain of EGFR in the 11 cell lines and 75 patients tested. The initial analysis of EGFRvIII expression by immunohistochemistry revealed that at least 50% of the patient tumors expressed EGFRvIII in a urothelial carcinoma tissue microarray. Conflicting reports exist, however, regarding the extent of EGFRvIII expression in tissues owing to the specificity of the antibodies and the methodologies used. Therefore, we sought to validate this observation by reverse transcription PCR, real-time PCR, and Western blot analysis. In these assays, none of the samples were positive for EGFRvIII except for control transfectants and glioblastomas. Conclusions: When our results are taken together, we conclude that alterations within the tyrosine kinase domain and expression of EGFRvIII are rare events in bladder cancer. The present study has clinical implications in selecting tyrosine kinase inhibitors for the therapy of urothelial carcinoma.

Tumor suppressor p53-dependent apoptosis is critical in suppressing tumorigenesis. Previously, we reported that DNA double-strand breaks (DSBs) at the V(D)J recombination loci induced genomic instability in the developing lymphocytes of nonhomologous end-joining (NHEJ)–deficient, p53-deficient mice, which led to rapid lymphomagenesis. To test the ability of p53-dependent cell cycle arrest to suppress tumorigenesis in the absence of apoptosis in vivo, we crossbred NHEJ-deficient mice into a mutant p53R172P background; these mice have defects in apoptosis induction, but not cell cycle arrest. These double-mutant mice survived longer than NHEJ/p53 double-null mice and, remarkably, were completely tumor free. We detected accumulation of aberrant V(D)J recombination–related DSBs at the T cell receptor (TCR) locus, and high expression levels of both mutant p53 and cell cycle checkpoint protein p21, but not the apoptotic protein p53-upregulated modulator of apoptosis. In addition, a substantial number of senescent cells were observed among both thymocytes and bone marrow cells. Cytogenetic studies revealed euploidy and limited chromosomal breaks in these lymphoid cells. The results indicate that precursor lymphocytes, which normally possess a high proliferation potential, are able to withdraw from the cell cycle and undergo senescence in response to the persistence of DSBs in a p53–p21–dependent pathway; this is sufficient to inhibit oncogenic chromosomal abnormality and suppress tumorigenesis.

Tumor suppressor p53-dependent apoptosis is critical in suppressing tumorigenesis. Previously, we reported that DNA double-strand breaks (DSBs) at the V(D)J recombination loci induced genomic instability in the developing lymphocytes of nonhomologous end-joining (NHEJ)-defi cient, p53-defi cient mice, which led to rapid lymphomagenesis. To test the ability of p53-dependent cell cycle arrest to suppress tumorigenesis in the absence of apoptosis in vivo, we crossbred NHEJ-defi cient mice into a mutant p53R172P background; these mice have defects in apoptosis induction, but not cell cycle arrest. These doublemutant mice survived longer than NHEJ/p53 double-null mice and, remarkably, were completely tumor free. We detected accumulation of aberrant V(D)J recombination-related DSBs at the T cell receptor (TCR) locus, and high expression levels of both mutant p53 and cell cycle checkpoint protein p21, but not the apoptotic protein p53-upregulated modulator of apoptosis. In addition, a substantial number of senescent cells were observed among both thymocytes and bone marrow cells. Cytogenetic studies revealed euploidy and limited chromosomal breaks in these lymphoid cells. The results indicate that precursor lymphocytes, which normally possess a high proliferation potential, are able to withdraw from the cell cycle and undergo senescence in response to the persistence of DSBs in a p53-p21dependent pathway; this is suffi cient to inhibit oncogenic chromosomal abnormality and suppress tumorigenesis.

V(D)J recombination is essential for the maturation of lymphocytes. Because of the involvement of cutting and joining DNA double strands, this recombination activity is strictly contained within the noncycling phases of the cell cycle. Such containment is crucial for the maintenance of genomic integrity. The ataxia telangiectasia mutated (ATM) gene is known to have a central role in sensing general DNA damage and mediating cell-cycle checkpoint. In this study, we investigated the role of ATM and its downstream targets in the cell-cycle control of V(D)J recombination in vivo. Our results revealed the persistence of double-strand breaks (DSBs) throughout the cell cycle in ATM À/À and p53 À/À thymocytes, but the cell-cycle regulation of a V(D)J recombinase, Rag-2, was normal. The histone variant H2AX, which is phosphorylated during normal V(D)J recombination, was dispensable for containing DSBs. H2AX was still phosphorylated at V(D)J loci in the absence of ATM. Therefore, V(D)J recombination, a physiological DNA rearrangement process, activates the ATM/p53 pathway to contain DNA breaks within the noncycling cells and surprisingly this pathway is not important for containing Rag-2 activity. This study shows the dynamic multiple functions of ATM in maintaining genomic stability and preventing tumorigenesis in developing lymphocytes.

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Purpose: To determine whether FDG PET can expand eligibility in biomarker-selected clinical trials by providing a means to quantitate response in patients with non-assessable disease by RECIST.Experimental Design: SUMMIT (NCT01953926) is a multicenter phase II "basket" trial of the Pan-HER kinase inhibitor, neratinib. Patients had advanced ERBB2 (HER2)-mutant solid tumors, !1 measurable lesion, preferably defined unidimensionally by RECIST v1.1, or alternatively metabolically by PET Response Criteria (PRC). The primary aim was to determine the proportion of additional breast cancer patients accrued using PRC who would have otherwise been ineligible based on RECIST criteria alone. The secondary aim was to determine the concordance of response versus non-response between RECIST and PRC.Results: Eighty-one patients with HER2-mutant metastatic breast cancer were accrued; 77 were evaluable for response by RECIST and/or PRC. 63 (82%) were RECIST-evaluable and 14 (18%) were accrued using PRC alone. Bone-only disease (n ¼ 11; 79%) was the most common reason for classification as non-measurable by RECIST. Twenty-nine patients were accrued and followed using both criteria, of which 25 (86%; 95% confidence interval, 68%-96%) were concordant for response versus non-response as defined by RECIST and PRC.Conclusions: PRC allowed patients with non-RECIST measurable disease access to therapy and facilitated more rapid accrual of patients to this trial of a rare biomarker. PRC and RECIST both provided methods of response assessment and were generally concordant. Thus, PRC was useful as a supplement to RECIST criteria. This provides a rationale for including FDG PET measurements in future clinical trials involving rare tumors or rare genomically defined subpopulations of more common cancers.