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Early Stage Lung Cancer: New Approaches to Evaluation and Treatment |
Authors' Affiliations: 1 Department of Internal Medicine, Division of Hematology/Oncology and 2 Department of Radiation Oncology, University of California, Davis Medical Center, Sacramento, California
Requests for reprints: David R. Gandara, UC Davis Cancer Center, University of California, Davis Medical Center, 4501 X Street, Suite 3016, Sacramento, CA 95817. Phone: 916-734-3772; Fax: 916-734-7946; E-mail: david.gandara{at}ucdmc.ucdavis.edu.
| Abstract |
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20% of cases, raising the issue of whether prophylactic cranial irradiation should be used after completion of chemoradiotherapy, similar to standard practice in limited stage small cell lung cancer (3). Cancer must be eradicated from all three compartments to achieve long-term survival. Four different treatment paradigms have emerged in recent years for application of chemoradiation (Fig. 1): sequential, concurrent, induction chemotherapy followed by concurrent chemoradiation, and concurrent chemoradiation followed by consolidation chemotherapy (4). Sequential approaches to chemoradiotherapy (5), in which chemotherapy precedes thoracic radiation, generally improve outcome by reducing distant failure rates, with no improvement in local control when compared with radiotherapy alone (6). In contrast, with concurrent chemoradiotherapy strategies, chemotherapy may play either a radiosensitizing role designed to improve local control or a cytotoxic role by eradicating distant micrometastases, or both, depending on the timing and doses of chemotherapy used. An example is provided by the trial of Schaake-Koning et al. (7) in which low-dose daily cisplatin improved survival solely by increasing local control without reduction in the rate of distant metastases. In view of these observations, concurrent chemoradiotherapy paradigms integrating both radiosensitizing agents and dose levels of chemotherapy effective against micrometastases may prove to be most efficacious.
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| Integration of Novel Therapeutic Agents into Chemoradiation Paradigms: Conceptual Issues |
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| Integration of Novel Therapeutic Agents into Chemoradiation Paradigms: Ongoing and Planned Clinical Trials |
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Signal transduction modulators of the epidermal growth factor receptor pathway. The epidermal growth factor receptor (EGFR), a member of the HER or Erb-B family of type I receptor tyrosine kinases, is implicated in the development and progression of cancer (8). EGFR is expressed in many normal human tissues and activation of this proto-oncogene results in overexpression in many types of human tumors. Recently, small molecule tyrosine kinase inhibitors (TKI, gefitinib and erlotinib) and monoclonal antibodies (cetuximab) directed against EGFR have been shown to be efficacious in the treatment of advanced NSCLC and colon cancer, respectively (9).
Because the EGFR TKIs gefitinib and erlotinib have been found to be active in patients with NSCLC after failure of frontline therapy, it was a logical step to combine them with chemotherapy. However, four large randomized trials of chemotherapy with or without gefitinib or erlotinib (INTACT 1 and 2, TRIBUTE, and TALENT) failed to show any benefit of the combination for response rate, progression-free survival, or overall survival (1013). The negative results of these trials represented a major setback for the field of NSCLC research. Several questions remained unanswered: Why did these trials fail? Are the results of these trials generalizable to anti-EGFR monoclonal antibody therapies? How do we best use EGFR inhibitors of either type (TKIs or monoclonal antibodies) in advanced NSCLC?
Possible explanations for the negative results of the INTACT, TRIBUTE, and TALENT trials include, but are not limited to, (a) lack of patient selection for a predictive marker of response; (b) incorrect dose, schedule, or sequence of drugs; (c) potential antagonistic interaction between concurrent EGFR TKI and chemotherapy; or (d) a combination of these and other factors. Despite previous reports of preclinical synergism between EGFR TKIs and chemotherapy, more recent in vitro and in vivo studies of concurrent administration have suggested antagonism when compared with sequential administration of EGFR TKIs and chemotherapy (14). In an in vitro model (Fig. 2), the greatest degree of apoptosis is achieved when the chemotherapeutic agent docetaxel and erlotinib are administered sequentially rather than concurrently. Similarly, in vivo data from a xenograft study are supportive of the concept of antagonism (Fig. 3). In this NSCLC experimental model, daily administration of gefitinib plus paclitaxel (D) achieves no better growth inhibition than either single agent alone (B or C). However, gefitinib given in pulse doses of 250 mg/kg on days 1 and 2 with the same schedule of paclitaxel (E) results in smaller average tumor volumes and increases the number of mice that are tumor free (15). This data suggests that antitumor activity of EGFR TKIs and chemotherapy may be schedule dependent.
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Lastly, it remains unclear whether the concerns described above pertain to monoclonal antibodies, such as cetuximab. In contrast to data with EGFR TKIs in the INTACT trials, cetuximab is effective in combination with concurrent chemotherapy in colorectal cancer (20). Moreover, the addition of cetuximab to radiation has recently been shown to be superior to radiation alone for locally advanced head and neck cancer (21). Based on these results, the Radiation Therapy Oncology Group is currently conducting a phase II study of cetuximab, carboplatin, paclitaxel, and radiotherapy in unresectable stage III NSCLC. A SWOG protocol in development will explore this approach with a combination of cetuximab given concurrently with thoracic radiation and weekly docetaxel in a defined population of patients with poor risk stage III NSCLC.
Angiogenesis inhibitors. Vascular endothelial growth factor (VEGF) is an endogenous angiogenic factor involved in both normal angiogenesis and the neovasculature associated with malignancy. In NSCLC, increased VEGF expression is associated with a poor prognosis and is inversely correlated with wild-type p53 (22). An anti-VEGF monoclonal antibody, bevacizumab, inhibits tumor-associated angiogenesis, growth, and metastasis in a dose-dependent manner. Preclinical studies have also shown synergistic antitumor activity for anti-VEGF antibody in combination with chemotherapy. Clinical trials have confirmed encouraging activity of bevacizumab in combination with chemotherapy in patients with metastatic NSCLC (23), and a randomized trial showed improved survival with the combination by comparison with chemotherapy alone in advanced-stage colorectal cancer (24). An ongoing phase II trial is evaluating bevacizumab in combination with paclitaxel/carboplatin and thoracic radiotherapy in stage III NSCLC.
Thalidomide was one of the earliest antiangiogenic agents to be tested in clinical trials. It is of historical interest because of its well-known teratogenicity, as evidenced by the stunted limb growth observed in children whose mothers took thalidomide as an antiemetic during pregnancy (25). One hypothesis was that these thalidomide-induced limb defects were due to angiogenesis inhibition in fetal limb buds. There has been a renewed interest in thalidomide during the past decade for its potential antineoplastic activity, initially noted in multiple myeloma (26). Thalidomide is currently being evaluated in an Eastern Cooperative Oncology Group phase III trial in which patients with unresectable stage III NSCLC are randomized to concurrent carboplatin/paclitaxel and radiation therapy with or without thalidomide.
Hypoxic cytotoxins. Tirapazamine, a hypoxic cell cytotoxin now undergoing clinical evaluation, shows preclinical synergism with chemotherapy and radiation (27, 28). Under aerobic conditions, such as in normal tissue, tirapazamine is inactive; however, it is bioactivated under hypoxic conditions. In an initial phase III trial in stage IV NSCLC (CATAPULT 1), tirapazamine in combination with cisplatin resulted in improved survival compared with cisplatin alone (29). In addition, it has shown promising clinical activity in combination with radiotherapy and cisplatin in head and neck cancer (30). Unfortunately, a subsequent phase III trial failed to confirm the superiority of tirapazamine plus chemotherapy versus chemotherapy alone (31). Present hopes for clinical utility of tirapazamine rest with ongoing trials using it in combination with radiotherapy. In stage III NSCLC, an ongoing trial of the NCI-sponsored California Cancer Consortium is testing tirapazamine in combination with concurrent carboplatin/paclitaxel and thoracic radiotherapy.
Cell cycle modulating agents. Tumor cell killing by ionizing radiation varies across the cell cycle. Cells are most radiosensitive in G2-M and most radioresistant in S phase. Therefore, agents that can increase cell numbers in G2 and block cells from entering S phase may be potential radiosensitizers. Similarly, many chemotherapy agents are cell cycle specific. NTAs that modulate the cell cycle offer tremendous potential as sensitizers for cell cyclespecific chemotherapeutic agents and radiotherapy. UCN-01, a staurosporine analogue isolated from Streptomyces, is an early example of this class of agents. UCN-01 was originally developed as an inhibitor of protein kinase C, but antitumor activity is more likely related to independent effects on cyclin-dependent kinase inhibition and cell cycle modulation. UCN-01 shows potent in vitro and in vivo activity against a variety of tumor types. In addition, UCN-01 markedly potentiates the cytotoxicity of several chemotherapeutic agents, including cisplatin. The mechanism of potentiation may be related to p53-independent abrogation of the typical G2 arrest induced by cisplatin (32). In NSCLC, UCN-01 is reported to enhance cisplatin-induced cytotoxicity 100-fold in a cell line in which UCN-01 alone is ineffective (33). Phase I trials of UCN-01 as a single agent have now been completed, and trials investigating combinations of UCN-01 and platinum-based chemotherapy will be initiated in the near future.
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| Open Discussion |
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Dr. Gandara: Yes, I agree, and that's why if these trials with cetuximab all turn out to be positive, then there is something different about EGFR monoclonal antibodies compared with the tyrosine kinase inhibitors, just as there is with the monoclonal antibody trastuzumab, which is additive with chemotherapy. For example, an immunologic response could be initiated through the monoclonal antibody that would not occur with a tyrosine kinase inhibitor.
Dr. Thomas Lynch: Dr. Johnson, for the patients with EGFR mutations who present with locally advanced disease, what are your thoughts on a trial design that might be a reasonable way to approach that group of patients?
Dr. Bruce Johnson: I think we need a prospective trial with the agent by itself so you know what the antitumor activity is. So, take a group of patients who have the mutation and have predominantly local disease, then treat them with concurrent radiation plus just the EGFR inhibitor.
Dr. Gandara: I didn't include that issue in my talk because you convinced me the mutation only occurs in 2% of our lung cancer patients in the United States, so we would have to do that trial in Japan.
Dr. Lynch: Two percent? Pasi Jänne's data presented at ASCO was 13% in those with metastatic disease. The question is how frequent is it in locally advanced disease?
Dr. Johnson: In the publication for our group, it was 2% [Science 2004;304:1497500]. We have another study in press of 250 patients and there the mutation runs
10%.
Dr. Lynch: The question is whether those patients present more often metastatically or more often with isolated nodules. I don't think we know if the stage distribution of EGFR mutants is the same as that of the whole population of lung cancer patients, although the hints we have so far suggest there is probably not a huge difference.
Dr. Joan Schiller: If it is only 10% though, it's going to be very difficult to do such a study.
Dr. Lynch: It's going to be incredibly difficult to do that. It becomes a Japanese question.
Dr. Karen Kelly: Paul Bunn made a comment to me the other day that there was no difference in overall survival in the TRIBUTE trial between the patients who had EGFR mutations and those who did not. Is that true?
Dr. Johnson: Of the
30 patients who had EGFR mutations, the survival is similar so far whether they got erlotinib or not. But there have only been four deaths in each group, so in terms of long-term outcome it is unknown as yet. If they had EGFR mutations and if they did or did not get erlotinib, the outcome of the people with advanced disease was dramatically different than those without mutations.
Dr. Vokes: If you take out those patients with the mutation, what happens to the rest of the group?
Dr. Lynch: The response rates in survival were not dramatically different in the group that had mutations and received erlotinib.
Dr. Gandara: Actually, the progression rate was dramatically different. If you did not have the mutation and you got concurrent erlotinib and chemotherapy, you had twice the progression rate compared with chemotherapy alone.
Dr. Lynch: You mean you did worse with the mutation? There was a higher response rate, 27% versus 21%.
Dr. Gandara: Yes. The response rate was higher, but the progression rate was dramatically higher if you got the combination and had no mutation.
Dr. Lynch: With all of these data, just like with the analysis we are doing with INTACT, it is a subset of a subset of a subset. It is retrospective, and you don't know the characteristics of the patients who you happen to have tumor on. Are those patients reflective of the entire group of people we see with metastatic disease? That is one of the concerns we have until we have prospective studies going forward.
Dr. Johnson: In the subset analyses of TRIBUTE, the take-home message to me is that the nonsmoker cohort has a dramatically different outcome from the smokers in that the median survival of the nonsmokers was 22 months compared with 10 months for the smokers. That is information we can actually use in treating patients.
| Footnotes |
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| References |
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This article has been cited by other articles:
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L. Paz-Ares, J.-Y. Douillard, P. Koralewski, C. Manegold, E. F. Smit, J. M. Reyes, G.-C. Chang, W. J. John, P. M. Peterson, C. K. Obasaju, et al. Phase III Study of Gemcitabine and Cisplatin With or Without Aprinocarsen, a Protein Kinase C-Alpha Antisense Oligonucleotide, in Patients With Advanced-Stage Non-Small-Cell Lung Cancer J. Clin. Oncol., March 20, 2006; 24(9): 1428 - 1434. [Abstract] [Full Text] [PDF] |
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