Chemicalinfo Chemlink Pharm-Chem Net

The treatment of non–small-cell lung cancer has made limited but clinically significant progress during the past two decades of clinical research. Through carefully designed clinical trials, investigators have identified several chemotherapeutic drugs to combat this disease. Many questions have been asked and answered. Which combinations work best? How frequently should they be given and for how long? And which patients should be treated?¹ Nonetheless, such advances have been limited, and the prognosis for patients with advanced disease remains grim.

Despite the modest results achieved with conventional cytotoxic chemotherapeutic agents, the past several decades of basic cancer research have started to yield therapeutic results based on our understanding of cancer biology. The identification of "druggable targets" has emerged from studies dissecting the mechanisms of tumor growth, invasion, and metastases; the evasion of apoptosis; self-sufficiency in growth signaling; insensitivity to antigrowth signals; sustained angiogenesis; and limitless replicative potential — the classic hallmarks of cancer.² Some therapies that target these pathways, such as agents inhibiting angiogenesis and cell-signaling pathways, are approved and in the clinic.

An example of how an understanding of basic cancer biology has translated into the clinic is that of the pathway of the epidermal growth factor receptor (EGFR), one of the four members of the HER2/ErbB family of receptors. Ligands bind to the receptor, inducing receptor dimerization and subsequent phosphorylation of intracellular tyrosine kinase–binding sites, leading to the activation of a cascade of downstream signaling events. Activation of these pathways leads to increased cellular proliferation, motility, adhesion, invasion, angiogenesis, and inhibition of apoptosis.³ Agents have been developed that inhibit this pathway by binding to the extracellular domain of the receptor, as in the case of monoclonal antibodies such as cetuximab and panitumumab, or by binding to the intracellular tyrosine kinase domain, such as erlotinib, gefitinib, and lapatinib.

However, these drugs do not work in everyone. Even though patients whose tumors have an activating mutation in the tyrosine kinase domain are likely to have a high rate of response to EGFR tyrosine kinase inhibitors and prolonged survival,⁴ these patients are in the minority. (Approximately 10% of patients in Europe and North America carry activating mutations.) Moreover, the emergence of secondary EGFR mutations that inhibit the binding of tyrosine kinase inhibitors has been observed in patients in whom resistance to such drugs has developed.⁵ Thus, the identification of patients who are most likely to benefit from EGFR inhibitors is key to the optimal use of these drugs so that patients who are unlikely to benefit are spared the side effects and the loss of time that could have been spent in pursuing more active agents.

Such identification of patients who are likely to respond to various drugs is central to "personalized medicine." Increasingly, patients are being treated by focusing on specific oncogenic pathways that are activated in their particular tumor rather than on the tumor's location or histologic features. Treating patients with drugs specific to their particular tumor is likely to yield increased response rates, prolonged survival, and a decrease in the number of patients who are exposed to toxic drugs unnecessarily. Although these additional tests may increase the initial cost of care, they may also prove to be cost-effective in the long term by reducing the costs associated with ineffective treatments.

To tailor patients' treatments to their tumors, however, one must have a sufficient quantity of tumor to test. Obtaining such quantities can be problematic, particularly for neoplasms such as lung cancer, in which the tumor is located in a visceral organ. Biopsies are often associated with complications, such as discomfort and risk of pneumothorax. The assessment of more accessible tissues, such as blood cells or skin, has not proved to be helpful as a surrogate for tumor biopsy. Thus, patients with suspected lung cancer often undergo procedures such as needle aspiration that frequently yield only sparse quantities of cytologic material. Obtaining adequate material for mechanistic studies and serial monitoring of tumor genotypes has been particularly challenging for patients with lung cancer and has been a major barrier to translating laboratory findings into therapy.

In this issue of the Journal, Maheswaran and colleagues describe the results of a study in which they isolated tumor-derived epithelial cells (circulating tumor cells) in 27 patients with metastatic non–small-cell lung cancer.⁶ Using a microfluidic device mediated by the interaction between circulating tumor cells and microposts coated with antibody against epithelial-cell adhesion molecule (EpCAM) under precisely controlled laminar-flow conditions,⁷ they were able to isolate circulating tumor cells from all 27 patients. Such cells represent a potential alternative to invasive biopsy as a source of cancer cells for genotypic studies and molecular characterization and for monitoring changes during therapy. However, since circulating tumor cells make up as few as 1 cell per 1x10⁹ hematologic cells in the blood of patients with metastatic cancer, the identification and isolation of these cells have been difficult.⁸ Although quantification of circulating tumor cells with the use of magnetic bead–conjugated antibodies against EpCAM has been approved by the Food and Drug Administration as a means of monitoring patients with metastatic breast and prostate cancer, its use in affecting treatment decisions is debatable.^9,10,11 Furthermore, the use of such cells for molecular studies has been limited by difficulties in isolating an adequate number of cells of sufficient purity in a reproducible manner.

In the microfluidic device (called the CTC-chip) used by Maheswaran et al., blood flows past EpCAM-coated microposts under conditions that optimize the capture of circulating tumor cells. The investigators used this device to isolate viable circulating tumor cells from virtually all the patients with metastatic cancer but not from healthy control subjects.⁷ In their study, they were able to identify EGFR activating mutations in 92% of patients with advanced lung cancer, and T790M, a mutation that confers drug resistance, in 55% of patients. In 12 patients for whom primary tumor samples, circulating tumor cells, and plasma were all available for analysis, genotyping of circulating tumor cells had a sensitivity of 92%. Perhaps more important, the investigators also showed that serial genotyping of circulating tumor cells seemed to have functional significance, since a decrease in the number of cells was correlated with a radiographic response to gefitinib in four patients, whereas an increase in the number of cells was correlated with the emergence of additional EGFR mutations and clinical progression.

The ability to detect genetic markers that guide treatment is obviously essential in identifying the appropriate therapy. Equally important, however, is the need to monitor tumor cells to determine whether the therapy is "hitting the target." When drugs that perturb pathways do not work, it is often unclear whether the lack of activity is due to an ineffective drug or a drug that does not reach its target or to a targeted pathway that is not a major factor in carcinogenesis. For decades, lung-cancer oncologists have been frustrated by difficulties associated with serially obtaining tumor tissue with which to determine whether molecular pathways in tumor cells are indeed being inhibited or otherwise affected in the manner predicted.

Whether the technique described by Maheswaran et al. will allow the isolation of viable cells of sufficient quantity and purity to identify treatment effects on cancer cells remains to be seen. One also wonders whether this technique will allow consistent detection and isolation of purified, viable circulating tumor cells from other tumor types and for molecular analysis of pathways other than that of EGFR. Moreover, this study represents a proof of principle, and the ease with which this approach can be used by others remains to be determined. That said, the capture and analysis of circulating tumor cells from patients with lung cancer represents a new diagnostic approach that may bring us closer to an era of individualized medicine.

Dr. Schiller reports receiving consulting fees from Genentech and Bristol-Myers Squibb and grant support from Genentech and doing uncompensated consulting work for Imclone. No other potential conflict of interest relevant to this article was reported.
Source Information

From the Division of Hematology and Oncology, Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas.

This article (10.1056/NEJMe0804521) was published at www.nejm.org on July 2, 2008. It will appear in the July 24 issue of the Journal.

References

1. Schiller JH, Harrington D, Belani CP, et al. Comparison of four chemotherapy regimens for advanced non-small-cell lung cancer. N Engl J Med 2002;346:92-98. [Free Full Text]
2. Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57-70. [CrossRef][ISI][Medline]
3. Jänne PA, Engelman JA, Johnson BE. Epidermal growth factor receptor mutations in non-small-cell lung cancer: implications for treatment and tumor biology. J Clin Oncol 2005;23:3227-3234. [Free Full Text]
4. Lynch TJ, Bell DW, Sordella R, et al. Activating mutations in the epidermal growth factor receptor underlying responsiveness of non-small-cell lung cancer to gefitinib. N Engl J Med 2004;350:2129-2139. [Free Full Text]
5. Kobayashi S, Boggon TJ, Dayaram T, et al. EGFR mutation and resistance of non-small-cell cancer to gefitinib. N Engl J Med 2005;352:786-792. [Free Full Text]
6. Maheswaran S, Sequist LV, Nagrath S, et al. Detection of mutations in EGFR in circulating lung-cancer cells. N Engl J Med 2008;359. DOI: 10.1056/NEJMoa0800668.
7. Nagrath S, Sequist LV, Maheswaran S, et al. Isolation of rare circulating tumour cells in cancer patients by microchip technology. Nature 2007;450:1235-1239. [CrossRef][Medline]
8. Krivacic RT, Ladanyi A, Curry DN, et al. A rare-cell detector for cancer. Proc Natl Acad Sci U S A 2004;101:10501-10504. [Free Full Text]
9. Braun S, Marth C. Circulating tumor cells in metastatic breast cancer -- toward individualized treatment? N Engl J Med 2004;351:824-826. [Free Full Text]
10. Cristofanilli M, Budd GT, Ellis MJ, et al. Circulating tumor cells, disease progression, and survival in metastatic breast cancer. N Engl J Med 2004;351:781-791. [Free Full Text]
11. Cristofanilli M, Hayes DF, Budd GT, et al. Circulating tumor cells: a novel prognostic factor for newly diagnosed metastatic breast cancer. J Clin Oncol 2005;23:1420-1430. [Erratum, J Clin Oncol 2005;23:4808.] [Free Full Text]