A comparative study of EGFR mutation screening methods in non-small cell carcinoma of lung

Epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase of the ERBB2 family that has important roles in the proliferation and metastasis of tumor cells. It is frequently overexpressed in common solid tumors and has become a favored target for orally administered small-molecule tyrosine kinase inhibitors (TKI) and monoclonal antibody-based therapy. Gain-of-function somatic mutations of the EGFR tyrosine kinase domain have been associated with the response of some patients with non-small-cell lung carcinoma to TKIs. We evaluated three methods of EGFR mutation analysis to identify an optimal assay for clinical testing based on comparison of diagnostic sensitivity, technical difficulty, and cost (Tab. 1, Fig. 1, Ref. 12).

Loss of Rap1GAP in papillary thyroid cancer

CONTEXT

Rap1 GTPase-activating protein (GAP) regulates the activity of Rap1, a putative oncogene. We previously reported Rap1GAP was highly expressed in normal human thyroid cells and decreased in five papillary thyroid carcinomas (PTCs).

OBJECTIVES

To confirm the significance of these findings, we analyzed Rap1GAP expression in a larger set of benign tumors (adenomas and hyperplastic nodules) and PTCs. We determined whether the presence of the BRAF(V600E) mutation or allelic loss of Rap1GAP related to changes in Rap1GAP protein expression. To determine the consequences of Rap1GAP loss, we targeted Rap1GAP in culture using small interfering RNA.

DESIGN, PATIENTS, AND METHODS

A highly specific Rap1GAP antibody was applied to sections of 55 human thyroid tissues. Genomic DNA was analyzed for the presence of the BRAF(V600E) mutation, and loss of Rap1GAP. Rap1GAP expression in rat thyroid cells was abolished using small interfering RNA.

RESULTS

We observed that down-regulation of Rap1GAP in benign lesions and PTCs was common. Rap1GAP expression was more severely decreased in PTCs. Loss of Rap1GAP expression was observed in multiple histological variants of PTCs. Approximately 20% of PTCs and adenomas exhibited allelic loss of Rap1GAP. Loss of Rap1GAP was not associated with the presence of the BRAF(V600E) mutation. In vitro, loss of Rap1GAP was sufficient to increase Rap1 activity in thyroid cells.

CONCLUSIONS

These data indicate that loss of Rap1GAP is a frequent event in PTC. The more frequent and greater down-regulation of Rap1GAP in PTCs compared with adenomas suggests a role for Rap1GAP depletion in the progression of human thyroid tumors, possibly through unrestrained Rap activity.

Phase II trial of sorafenib in advanced thyroid cancer

PURPOSE

Given the molecular pathophysiology of thyroid cancer and the spectrum of kinases inhibited by sorafenib, including Raf kinase, vascular endothelial growth factor receptors, platelet-derived growth factor receptor, and RET tyrosine kinases, we conducted an open-label phase II trial to determine the efficacy of sorafenib in patients with advanced thyroid carcinoma.

PATIENTS AND METHODS

Eligible patients with metastatic, iodine-refractory thyroid carcinoma received sorafenib 400 mg orally twice daily. Responses were measured radiographically every 2 to 3 months. The study end points included response rate, progression-free survival (PFS), and best response by Response Evaluation Criteria in Solid Tumors.

RESULTS

Thirty patients were entered onto the study and treated for a minimum of 16 weeks. Seven patients (23%; 95% CI, 0.10 to 0.42) had a partial response lasting 18+ to 84 weeks. Sixteen patients (53%; 95% CI, 0.34 to 0.72) had stable disease lasting 14 to 89+ weeks. Seventeen (95%) of 19 patients for whom serial thyroglobulin levels were available showed a marked and rapid response in thyroglobulin levels with a mean decrease of 70%. The median PFS was 79 weeks. Toxicity was consistent with other sorafenib trials, although a single patient died of liver failure that was likely treatment related.

CONCLUSION

Sorafenib has clinically relevant antitumor activity in patients with metastatic, iodine-refractory thyroid carcinoma, with an overall clinical benefit rate (partial response + stable disease) of 77%, median PFS of 79 weeks, and an overall acceptable safety profile. These results represent a significant advance over chemotherapy in both response rate and PFS and support further investigation of this agent in these patients.

Downregulation of Rap1GAP contributes to Ras transformation

Although abundant in well-differentiated rat thyroid cells, Rap1GAP expression was extinguished in a subset of human thyroid tumor-derived cell lines. Intriguingly, Rap1GAP was downregulated selectively in tumor cell lines that had acquired a mesenchymal morphology. Restoring Rap1GAP expression to these cells inhibited cell migration and invasion, effects that were correlated with the inhibition of Rap1 and Rac1 activity. The reexpression of Rap1GAP also inhibited DNA synthesis and anchorage-independent proliferation. Conversely, eliminating Rap1GAP expression in rat thyroid cells induced a transient increase in cell number. Strikingly, Rap1GAP expression was abolished by Ras transformation. The downregulation of Rap1GAP by Ras required the activation of the Raf/MEK/extracellular signal-regulated kinase cascade and was correlated with the induction of mesenchymal morphology and migratory behavior. Remarkably, the acute expression of oncogenic Ras was sufficient to downregulate Rap1GAP expression in rat thyroid cells, identifying Rap1GAP as a novel target of oncogenic Ras. Collectively, these data implicate Rap1GAP as a putative tumor/invasion suppressor in the thyroid. In support of that notion, Rap1GAP was highly expressed in normal human thyroid cells and downregulated in primary thyroid tumors.

Sorafenib targets BRAF and VEGFR in metastatic thyroid carcinoma

6019

Background. There is no effective therapy for patients with metastatic thyroid cancer not cured by surgery or treatment with I131. Sorafenib is a promising multi-tyrosine kinase inhibitor for patients with metastatic PTC (mPTC). Although the primary targets of sorafenib are thought to include BRAF and VEGFR, this has been the subject of debate. Whether sorafenib primarily acts on the tumor cells (TC) or endothelial cells (EC) and how BRAF mutation status (45% of PTC harbor V600E) relates to response is also unknown. Methods. Responses of patients with metastatic, iodine-refractory PTC, enrolled into our phase II study of sorafenib were monitored by PET at 4 wks and CTs every 2 mos. Sorafenib activity was studied using immunohistochemistry (IHC) for pERK, pAKT, and pVEGFR-2, while Ki-67 showed proliferating cells in tumor tissue pre- and on treatment. BRAF mutation status was determined by DNA sequencing. Results. Of 15 patients, five patients achieved a PR, three are stable (SD), two progressed, and three patients with SD withdrew due to toxicity. Target lesions decreased on average 31%. Eight of 10 PET scans showed decreased activity at 4 weeks. IHC on tissue from 2 patients (at 1 and 2 wks, both BRAFwt) showed 50% decrease in pERK (downstream of VEGFR2 and BRAF) and 30% decrease in pAKT (downstream of VEGFR2). p-ERK and p-AKT were altered in both the TC and EC. Ki-67 decreased from 10% to <1%. No change in VEGFR-2 was seen; but, pVEGFR-2 completely disappeared in one sample while the other showed a small decrease. Quantitative analysis using a multispectral imaging system confirmed the changes observed by IHC. In tissue from a patient at 17 months on sorafenib, the decrease in pERK and pAKT appeared to be the same or reversed, suggesting compensatory changes in these pathways in resistant but stable disease. Conclusions. Our study shows the early clinical and biologic activity of sorafenib in patients with mPTC and the targets of early suppression. Importantly, it also reveals compensatory changes in target molecules in cells resistant to therapy. These cells are the likely source of tumor resistance that has been seen to develop to other similar targeted agents. Sorafenib is the first viable treatment option for patients with mPTC, and these results provide key insights into the mechanisms of action and resistance of this drug.

No significant financial relationships to disclose.

Lack of BRAF mutations in hyalinizing trabecular neoplasm

The hyalinizing trabecular neoplasm (HTN) of the thyroid is an unusual and controversial lesion. Some consider it a peculiar type of papillary thyroid carcinoma (PTC) because of its nuclear features and presence of psammoma bodies. Others consider it an adenoma. Molecular studies have found RET/PTC translocations in some examples, supporting HTN as a PTC; however mutations in BRAF (another marker for PTC) have not been found.

We report two cases of classic HTN and a case of trabecular PTC and show BRAF mutations in the latter and not in HTN. Trabecular growth pattern is insufficient for a diagnosis of HTN and lesions with such a pattern and nuclear features of PTC are cancers. Morphologically classic HTN are not associated with metastatic potential and should be considered adenomas.

Epidermal growth factor receptor (EGFR) mutations in breast and cervical cancer

20101

Background: EGFR is a tyrosine kinase receptor in the HER family which is widely expressed in a number of epithelial tumors and is believed to play a key role in cell proliferation. Molecular analysis of the EGFR gene in patients with non-small-cell lung cancer have identified a distinct subset of tumors that possess specific point mutations in the tyrosine kinase region of the EGFR gene, which correlate to response to tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib. Clinical trials involving TKIs are currently under way for patients with breast and cervical cancer. While responses thus far may have been modest it is unclear whether specific EGFR mutations are present in breast and cervical cancers which identify patients with improved prognosis and better response to therapy in these cancers. Using clinical samples with 5 years of follow-up clinical data, we have set out to determine whether EGFR mutations exist in breast and cervical cancers, and how these mutations, if any, correlate with the clinical data. Methods: We plan to perform sequence analysis of the tyrosine kinase domain of the EGFR gene (exons 18–24) in 50 archival breast and 44 cervical cancer specimens using PCR amplification and sequencing of genomic DNA. Clinical information has been extracted from patient charts on samples and will be correlated with the presence of any EGFR mutations identified. Results: To date we have collected 50 breast and 44 cervical tumor blocks and have isolated genomic DNA from the specimens. Sequencing for point mutations in exons 18–24 is underway. Clinical data on the cervical cancer specimens revealed a mean age at diagnosis of 48.2 years, tumor grades that were mostly intermediate (50%) and high (45%), and all FICO stages at diagnosis (43% stage I, 30% stage II, 5% stage III, 5% stage IV). In addition the rate of recurrence was 32%, and survival rate was 82% with an average time of follow-up for the set of 4.9 years. Conclusions: Our data will further elucidate the role of point mutations in EGFR gene in breast and cervical cancer prognosis and response to therapy, and will complement data currently being collected in clinical trials using TKIs.

No significant financial relationships to disclose.

Importance of anatomical subsite in correlating risk factors in cancer of the oesophagus--report of a case--control study

In Bangalore, cancer of the oesophagus is the third most common cancer in males and fourth most common in females with average annual age-adjusted incidence rates of 8.2 and 8.9 per 100,000 respectively. A case-control investigation of cancer of the oesophagus was conducted based on the Population-based cancer registry, Bangalore, India. Three hundred and forty-three cases of cancer of the oesophagus were age and sex matched with twice the number of controls from the same area, but with no evidence of cancer. Chewing with or without tobacco was a significant risk factor. In both sexes chewing was not a risk factor for cancer of the upper third of the oesophagus. Among males, non-tobacco chewing was a significant risk factor for the middle third but not for the other two segments and tobacco chewing was a significant risk factor for the lower third of the oesophagus, but not for the other two segments. Bidi smoking in males was a significant risk factor for all three segments being highest for the upper third, less for the middle third and still less for the lower third. The risk of oesophageal cancer associated with alcohol drinking was significant only for the middle third.