The criteria used to identify patients with non-small-cell lung cancers (NSCLCs) who can benefit from treatment with crizotinib may omit an estimated 8.5 percent of patients who could benefit from the drug, according to research published in the November 15 issue of Cancer (2013;119:3968-3975).
“Part of the natural history of developing personalized medicine is that we will always initially focus on biomarkers that capture most of the people who respond to a drug,” said the lead author, D. Ross Camidge, MD, PhD, Investigator at the University of Colorado (CU) Cancer Center and Director of the Thoracic Oncology Clinical Program at CU Hospital. “But spotting most is not the same as all. If we don't want to deny people effective treatments, we then have to do additional grunt work to identify everyone who will benefit.”
Still, Nathan Pennell, MD, PhD, of the Department of Solid Tumor Oncology at Cleveland Clinic, said, it remains to be seen how relevant the findings are in actual clinical practice.
Similarly, also asked for his opinion, Eric Bernicker, MD, of the Department of Thoracic Medical Oncology at Houston Methodist Cancer Center said, “To my way of thinking, this study is hypothesis-generating.”
For the research, Camidge and his colleagues assessed 1,426 NSCLC specimens tested for ALK using Vysis break-apart fluorescence in situ hybridization (FISH) between October 2008 and December 2010 at the Colorado Molecular Correlates laboratory, including 174 that were positive for an ALK rearrangement and 1,252 that were negative.
ALK-positive cells were identified in zero to nine percent, 10 to 15 percent, 16 to 30 percent, 31 to 50 percent, and more than 50 percent, in 79.3 percent, 8.5 percent, 1.4 percent, 2.7 percent, and 8.1 percent of the clinical specimens, respectively. Specimens that fell within the range of 10 to 15 percent were considered borderline negative.
The researchers also found an increased native ALK copy number in 19 percent of ALK-positive tumors and 62 percent of ALK-negative tumors. An increased copy number, though, did not correlate with sensitivity to crizotinib in cell lines, the results showed.
Finally, the team reported that up to six percent of tumor cells contained atypical negative genetic patterns—for example, 3' ALK doublets or single 5' ALK.
Importance of a Cutoff
Asked to give some background, Bilal Piperdi, MD, Director of Thoracic Medical Oncology at Montefiore Einstein Center for Cancer Care, explained that ALK-positive tumors represent only a small fraction of lung cancers—about three to seven percent—and that crizotinib targets NSCLC tumors fairly effectively when patients have an ALK translocation together with a fusion of the gene echinoderm microtubule-associated protein-like 4 (EML4).
Crizotinib was FDA-approved for use in these patients once they have undergone ALK status testing using FISH with the Vysis break-apart probe set. As is the situation with any assay, physicians need some cutoff to see who is positive and who is negative, and the cutoff used for this particular test is when at least 15 percent of tumors cells on the slide are positive or when the pathologists observes the break-apart signal in the cells, he said.
“But there's a continuum. What if patients are at exactly 15 percent? What about 13 percent, 14 percent, or 10 percent? This paper suggests very few borderline cases exist, and that most are clear cut at less than 10 percent or more than 20 or 30 percent. This paper demonstrates that the cutoff of 15 percent of cancer cells having the split apart signal seems relatively reasonable.”
Pennell said, “Essentially, what the researchers did was look at their very large panel of ALK-positive and ALK-negative patients to see if they could better define a cutoff on whether a tumor sample was truly positive or negative. The strength of the study is that it's the largest bank of ALK-positive non-small cell lung cancer specimens that has ever been examined in this way.”
Sometimes FISH indicates gene amplification or polysomy of ALK oncogene in cancer cells, Piperdi said of the increased ALK copy number that the study investigators observed. Researchers often see multiple copies of the ALK gene that are not necessarily translocated, he said. “But we don't know what this means exactly. Does it have any clinical meaning? Will the patient respond to treatment?”
The paper demonstrates that patients who do not have the ALK translocation have more “copy number gain” compared with that in ALK-positive patients, he continued. However, the in vitro cell line data provided in the study indicated that ALK-negative tumors with a higher copy number were not sensitive to crizotinib—“This is a very important message, and we've also been looking at this issue at our own institution.”
Pennell maintained that while the researchers had hypothesized that an increase in the mean native ALK copy number in ALK-negative tumors would indicate a new population of patients who could benefit from crizotinib, based on their cell line testing, “this isn't a biomarker that shows patients can benefit from the agent.”
From a biological perspective, the polysomy observed in ALK translocation negative versus positive tumors is usually a sign of the genomic instability common in smokers and typical forms of lung cancer, Piperdi noted. “We don't see that much polysomy in ALK-positive tumors, which may be more genomically stable compared with regular garden-variety tumors.” In these more common ALK-negative tumors, although multiple copies of ALK are present, the tumor is not dependent on an ALK signal for survival, and that is probably why crizotinib doesn't work, he said.
Essentially, the protein overexpression in ALK-negative tumors reflects “the wheels coming off the bus across the genome and the heterogeneous content of cells,” Bernicker said.
Further Testing for Borderline Patients
Camidge said that while the current cutoff of 15 percent for FISH testing is reasonable and does not immediately need to be changed, patients scored as borderline-negative should undergo further testing—for example, immunohistochemistry—to determine if they are actually positive and might benefit from crizotinib. “We need to explore some of these people who are just below the cutoff point and come up with some more evidence-based definition of who responds to the drug and who doesn't.”
Patients who are borderline should probably undergo further testing with either polymerase chain reaction or immunohistochemistry to determine whether they do or do not have the EML4-ALK translocation, Piperdi agreed. “There needs to be very clear communication between pathologists and oncologists, and FISH assay tests need to be done in centers with a lot of experience.”
And Pennell emphasized that while the study suggests that patients in the 10 to 15 percent range could perhaps benefit from a second test, “we don't have any clinical outcomes on this yet.”
What oncologists need to know is whether these borderline individuals respond well to current ALK therapies such as crizotinib or LDK378, currently being evaluated by Novartis, Bernicker said. “This is an interesting paper, and we clearly need to move forward to see whether borderline patients have a response to these therapies.
“Even though it's not a huge absolute number, the bottom line is if you're a patient, you would sure like to know if you could benefit from these drugs before going on to chemotherapy.”
Atypical Negative Patients
Camidge and his colleagues also note that additional testing may be needed in patients whose tumors cells contain atypical negative genetic patterns. These cells do not meet the break-apart positivity criteria, but could contain complex rearrangements, some of which might be associated with driving the cancer, he said. “So, while you have someone who is clearly ALK-negative in terms of the 15 percent cutoff, they may still, biologically, be positive due to these patterns.”
He noted that University of Colorado oncologists recently identified one of these atypical patterns in an ALK-negative patient who was seeking a second opinion at their center. The patient, who had been identified as atypically negative through a FISH assay, underwent additional testing with immunohistochemistry, was identified as positive, and subsequently received crizotinib and responded to the drug.
Still, Bernicker said, although scientifically interesting, atypical negative tumors were “very small in number [in this study], and I'm not sure this knowledge is of clinical help.” However, more information about these tumors is likely to be pursued in the research setting, he said.