Lung cancer causes 160,000 deaths
each year – more than the next four cancers combined. Diagnostic and treatment
options have improved greatly in the past decade and continue to advance at a
rapid rate. Among the most important advances have been: Learning that
chemotherapy combinations of a platinum-containing drug produce substantial
improvements in tumor shrinkage, quality of life and extension of life. Second,
these combinations, when added to surgery and/ or radiation for early stage
disease, improve survival and increase cure rates. Third, the introduction of
“Targeted” drug therapies have led to often dramatic tumor shrinkage and
increased disease free survival. Patients who develop lung cancer which has
spread still generally die within a year of diagnosis but progress is apparent
and improvements are developing quickly.
Drug therapy for lung cancer had
been disappointing until recent years. The combination of platinum containing
compounds such as cisplatin or carboplatin with drugs like premetrexed,
docetaxel, paclitaxel or gemcitabine have substantially improved the response
rates, progression-free survival and the overall duration of survival as well
as reduce symptoms from lung cancer. Most
patients will have substantially less pain, less difficulty breathing, and
reduced cough, among relief of other symptoms as well. Whereas only 10% of
patients with advanced non-small cell lung cancer (NSCLC) will live for one
year with “supportive care” alone, approximately 50% will survive one year with
current chemotherapy. However, virtually all patients with advanced lung cancer
still die within 3 years of diagnosis. So
a major advance but still a long ways to go.
For patients with limited small
cell lung cancer (SCLC) or those with localized or locally advanced NSCLC,
chemotherapy has a vital and potentially curative role. In combination with
radiation therapy, approximately 25-30% of patients with localized SCLC or
NSCLC can be cured. In selected patients with localized NSCLC, surgery may
incrementally improve outcome, though this is controversial. The use of
multimodality therapy in these diseases has been one of the major advances in
oncology in the past 25 years.
Another major
advance in drug therapy of lung cancer today is the development of so called
“targeted” drugs. Many cancers have mutations or rearrangements in their DNA
that in turn produce an abnormal protein – a protein that can initiate cancer,
lead to its proliferation or its metastatic potential. These are changes in the
DNA of the tumor itself that are critical to the initiation and progression of
the cancer, hence the term “driver” mutations. A targeted drug is one that
attacks or binds these abnormal proteins that are directly causing or
encouraging the growth of the tumor. Among patients with lung adenocarcinoma
(which represent about 40% of lung cancers), about 17 percent have a mutation
of a tyrosine kinase receptor gene called EGFR (epidermal
growth factor receptor), about 22 percent have KRAS (Kirsten rat
sarcoma viral oncogene ) mutations and perhaps 5
percent have an EML4 (echinoderm microtubule-associated
proteinlike4) rearrangement with the ALK (anaplastic
lymphoma kinase) gene. There are at least seven other of these mutations
or rearrangements, each occurring uncommonly and it is likely that many more
will be detected in the years to come. These three mutations/rearrangements
appear to be mutually exclusive and occur very rarely in the other forms of
non-small cell lung cancer (NSCLC), i.e., squamous cell and large cell tumors.
Since these DNA gene changes direct the formation of abnormal proteins, inhibiting
the protein action by a targeted drug can lead to shrinkage of the cancer or
slowing of its progression, often with rather dramatic success.
These driver
mutations make it possible to categorize many adenocarcinomas based on
molecular variations. It is instructive to appreciate that although a group of
tumors may appear identical by histology under the microscope, they are
actually distinct subtypes of lung cancer with different responses to the
available therapies. This helps to explain why patients with equivalent staged
and histologic tumors may respond much differently to the same treatment. It is
clear that at least adenocarcinoma (and presumably squamous and large cell will
follow suit shortly) should be molecularly typed before undertaking treatment.
Patients
whose tumors have one of these mutations have a greater likelihood of
responding to the corresponding targeted receptor inhibitor. Among the EGFR
tyrosine kinase inhibitors are the new drugs erlotinib (Tarceva), gefitinib (Iressa) and
afatinib (Tomtovok). Though
these drugs may be dramatically effective in reducing disease burden, it is
important to note that drug resistance will develop over time in virtually all
patients. The average patient experiences about one year of benefit for
erlotinib and similar agents. There are some patients (about 5-10%) who may
benefit for several years. Newer drugs are under development that can be used
once resistance develops. A recent trial compared erlotinib to the current
standard chemotherapy of platinum-based therapy for initial treatment of EGRF
positive adenocarcinoma patients. The median progression-free survival was 10.4
versus 5.1 months.
There are no
targeted drugs for KRAS at this time however there is one for those with ALK
rearrangements. Crizotinib (Xalkori)
was approved by the FDA based on results among patients with EML4-ALK fusions
who had a better than 50 percent response rate that persisted for nearly a year
despite this being second line treatment (i.e., the patient had already received
prior therapy and had had their disease progress before trying this drug). Compared
to standard combination chemotherapy, the response rate was 65 percent compared
to 20 percent and side effects were generally modest. Only 3 -5 percent of lung
cancer patients have the ALK+ gene rearrangement so that equates to maybe
50,000 patients worldwide per year. But for these relatively few patients,
crizotinib has become the new standard for first line therapy. There are also
some additional new drugs in the pipeline that are ALK+ inhibitors. These may
prove effective for those that develop resistance to crizotinib as essentially
all of these tumors eventually will do.
A separate
approach is to target the growth of blood vessels since the tumor needs a
steady supply of nutrients to persist and progress. Affecting such
“angiogenesis” might prove of value. Bevacizumab (Avastin) is a monoclonal
antibody that attacks vascular endothelial growth factor (VEGF), a molecule
that encourages the growth of small vessels. It has been found to add a few
months to progression free survival when used with cisplatin and paclitaxel for
non-squamous NSCLC. Overall survival was increased from 10.3 months with
cisplatin and paclitaxel alone to 12.3 months with the three drug combination. Avastin
has not demonstrated any advantage when added to other chemotherapy regimens. The
current approach is to use it as first line therapy with a platinum based
combination of drugs and after maximum response to continue it until relapse or
progression of disease. Avastin costs about $100,000 per year.
There are
multiple messages here.
·
First, the combination of
platinum-based combinations has markedly improved the treatment of late stage
lung cancer.
·
Second, chemotherapy combined with
radiation for early stage disease offers an increased opportunity for cure.
·
Third, certain patients, principally
those with adenocarcinoma, will have one of these “driver” mutations in their
tumor DNA. Knowing what is driving the cancer may be the most important
development of recent years.
·
Fourth, new drugs have and continue
to become available that inhibit these abnormal proteins resulting in
meaningful shrinkage and occasional complete responses.
·
Firth, the responses, although
heartening, can be but are usually not long lasting and come with various
toxicities that can be quite serious.
·
Equally important, sixth, knowing
that a specific mutation exists – or does not exist – can save a patient time,
the expense and the toxicities of receiving a drug that is destined to be inactive.
·
Seventh, and quite important, the
technologies to test for these mutations are new and not fully understood as
yet. It is clear that it is not a matter of pushing a simple “on/off” switch.
But it is a definite start with improvements of a degree and duration not seen
previously in this disease.
·
Eighth, it may well be, just as with
cancer chemotherapy, that combinations of targeted drugs or targeted compounds
plus standard chemotherapy will be found to be more effective and lead to more
long lasting responses.
·
Finally is the issue of cost. Combinations such as platinum/paclitaxel or
platinum/gemcitabine are inexpensive as the drugs are off patent. But the new
targeted drugs are each highly expensive. This raises the question of whether and when
this level of expense is justified for a relatively short period of time
without the cancer progressing or with such limited added survival. Some
countries such as the British have refused to cover the expense of Avastin for
lung cancer citing that it does not cure but is highly expensive. In the USA,
some commercial insurance likewise will not pay for some of these highly
expensive drugs. The pharmaceutical companies maintain however that the
response rates justify the costs and that the prices are appropriate given the
expense of developing these new compounds.
Although there is obviously room
for improvement, it is clear that there has been major progress in the drug
treatment of lung cancer. The rate of development of new approaches has been
rapid and can be expected to continue.
The next and last of this series
will discuss the importance of multi-disciplinary care, palliative care and
seeking high levels of expertise combined with compassion and caring.