The Tumor Biomarker Series: EGFR

Epidermal growth factor receptor (EGFR) is the most frequently amplified oncogene in astrocytic tumors (>40% or GBMs and 5-10% of anaplastic astrocytomas). EGFR is far more often amplified in de novo GBMs as compared to secondary GBMs. About one-half of those GBMs with EGFR amplification also have specific EGFR mutations (the vIII mutant), which produce a truncated receptor with constitutive activity. Both EGFR amplification and EGFRvIII mutant are mutually exclusive with IDH mutations. So, what is the utility of EGFR testing? First, astrocytomas with EGFR amplification tend to be of higher grade. So if, for example, the diagnostician is vacillating between a WHO grade II and a WHO grade III tumor, positive EGFR amplification status would favor the latter. Secondly, EGFR amplification can also help distinguish between a small cell GBM (which would potentially harbor the amplification) from anaplastic oligodendrogliomas (which do not exhibit the amplification).

"Bad Ass" CrossFitter and Neuropathologist Greg Fuller set to compete in kettlebell competition for brain cancer research

Elite Neuropathologist

Elite Athlete

It's no secret that Dr. Greg Fuller (pictured) is the fittest neuropathologist in the world. What his colleagues might not know is that he is the 67th fittest man in the world for his age class (60+). Greg's wife, Tina, describes him as a "bad ass CrossFitter". As a former owner of a CrossFit "box" myself, I know what it takes to achieve Greg's level in the Sport of Fitness. It requires true grit. There are many of us who would also consider Greg a "bad-ass neuropathologist" -- in the very best sense of that phrase. He's bringing together his love of fitness with his commitment to the study of CNS malignancies by participating in the Kettlebells For Brain Cells competition in Boerne, Texas on June 13. (So, he has a legitimate reason for not showing up at the concurrent AANP annual meeting. in Denver.) All proceeds from the competition will be going to the American Brain Tumor Association. The event is being organized by a brain tumor patient at MD Anderson Cancer Center, where Greg is Chief Neuropathologist. This is a shining example of a neuropathologist reaching out to a patient in a very personal way. Best of luck in the competition, Greg. Crush it!

The Tumor Biomarker Series: Ki-67

An immunohistochemical marker of cellular proliferation, the nuclear antigen Ki-67 is positive in cells that are actively engaged in cell cycle (i.e., not in G0). Results are expressed as a percent index of positively staining cells. Several studies have shows a correlation between Ki-67 indices in various astrocytomas, oligodendrogliomas, and mixed gliomas. Among grade II and grade III diffuse gliomas, the Ki-67 index provides prognostic value. However, investigations have consistently shown that Ki-67 proliferation indices have no prognostic value on patient outcomes for GBM. So, if you have an unmistakable GBM under your microscope, you are not practicing evidence-based parsimonious medicine by ordering Ki-67 immunohistochemistry on that tumor.  On the other hand, if you are debating between diagnosing a grade III or a grade IV astrocytoma, Ki-67 can be helpful in swaying your decision. The Ki-67 index is not used in the WHO grading system because of the high degree of technical variability between laboratories, making standardization difficult.

The Tumor Biomarker Series: ATRX

Alpha Thalassemia/Mental Retardation Syndrome X-linked (ATRX) is a gene that encodes a protein involved in chromatin remodeling. ATRX mutations are a marker of astrocytic lineage among the IDH-mutant gliomas and are mutually exclusive with 1p/19q codeletion. Present in 57% of secondary GBMs, ATRX mutations are uncommon in primary glioblastomas. Nearly all diffuse gliomas with IDH and ATRX mutations also have TP53 mutation and are associated with the Alternative Lengthening of Telomeres (ALT) phenotype. Immunohistochemistry for ATRX demonstrates loss of protein expression in neoplastic cells harboring the inactivating mutations, while expression is retained within non-neoplastic internal controls (such as endothelial cells).

The Tumor Biomarker Series: PTEN and LOH of chromosome 10

Loss of heterozygosity (LOH) of chromosome 10 occurs in most GBMs and less frequently in grade II and III diffuse astrocytomas. The phosphatase and tensin (PTEN) gene at 10q23.3 has been most strongly implicated as a glioma-related tumor suppressor on chromosome 10q, with PTEN mutations identified in about 25% of GBMs and less frequently in grade III astrocytomas. Losses of chromosome 10 and mutations in PTEN are considered to be specific for astrocytic differentiation and are rare in oligodendrogliomas. They are also markers of high-grade progression and aggressive clinical behavior in astrocytomas.

The Tumor Biomarker Series: BRAF

Aberrant constitutive activation of BRAF tends to be seen in cerebellar and midline pilocytic astrocyomas whereas the activating point mutation at BRAF V600E is more likely to be seen in cerebral examples. The V600E point mutation is also observed in other low-grade gliomas and glioneuronal neoplasms, including approximately two-thirds of pleomorphic xanthoastrocytomas, and lower percentages of ganglioglioma, desmoplastic infantile ganglioglioma, dysembrioplastic neuroepithelial tumor, and papillary craniopharyngioma. Although less common, diffusely infiltrative gliomas including glioblastoma, particularly the epithelioid variant, may also demonstrate the V600E point mutation -- making this biomarker potentially less useful as a diagnostic tool in distinguishing low-grade gliomas from high-grade ones.

The Tumor Biomarker Series: MGMT

MGMT stands for O6-methylguanine-DNA methyltransferase. I must admit that this is my favorite biomarker only because of its cool mechanism of action.  The standard chemotherapy for gliomas is temozolomide, which acts by cross-linking DNA through alkylating multiple sites including the 06 position of guanine. Crosslinking at this site is reversed by the DNA repair enzyme MGMT. Thus, low levels of MGMT activity by GBM cells is associated with enhanced response to alkylating agents such as temozolomide. To a large degree, the activity level of MGMT is determined by the methylation status of the gene's promoter. MGMT can be epigenetically silenced by hypermethylation. About half of all GBMs are epigenetically silenced in this manner and are therefore more susceptible to the alkylating action of temozolomide.  The methylation status of MGMT can be assessed by PCR-based testing. In addition to predicting better response to temozolomide, investigators have shown that epigenetic gene silencing of MGMT is a strong predictor of prolonged survival independent of treatment.

The Tumor Biomarker Series: TP53

A few month ago, the College of American Pathologists released a Template for Reporting Results of Biomarker Testing of Specimens from Patients with Tumors of the Central Nervous System. Therefore, I thought it would be a good idea to review as succintly as possible the various tumor biomarkers one could use to interrogate CNS tumors. Not all neuropathologists would agree as to which ones, if any, are essential. So, comments are most welcome! The first biomarker I'd like to address is TP53, mainly because I have doubts about it's utility -- except for cases where there is a question regarding whether or not an oligodendroglial component is present. However, immunohistochemical p53 testing is performed on virtually all high-grade astrocytomas at many institutions. Here's a summary of the CAP consensus description of the TP53 test:

Found in a majority of high-grade astrocytic tumors, TP53 mutation is rare in oligodendrogliomas. Mutation of TP53 is highly correlated with IDH mutation. As a surrogate for testing the actual TP53 mutation, p53 immunohistochemistry is typically performed. As for the utility of this test, the CAP template makes the following statement: "[T]here is a strong association between IDH1 mutation and TP53 mutation in diffuse astrocytomas and this combination of mutations is helpful in distinguishing astrocytomas from oligodendrogliomas."

My feeling is that if you have a histomorphologically classic pure astrocytic neoplasm, there is no need for p53 immunohistochemistry. And, yet, you almost always see p53 immunohistochemistry results on reports for classic glioblastomas, anaplastic astrocytomas, and infiltrative astrocytomas. I just don't get it. Even in cases where you have a question about the presence of an oligodendroglial component, testing for IDH1 mutation and 1p/19q deletion would be more helpful than testing for IDH1 and TP53. I would love to hear from people who could dissuade me of this opinion regarding the utility of p53 immunohistochemistry. Feel free to enter comments below.

Best Post of November 2014: Robin Williams had Lewy Body Diesease

The next in our "Best of the month" series is from November 18, 2014:

Robin Williams

The official cause of Robin Williams' death, released Friday by the Marin County coroner, was ruled

Williams had long battled alcoholism, drug addiction and depression, but in November 2013 he was diagnosed with Parkinson's disease, according to his widow, after noticing a tremor in his left arm and difficulty moving on his left side as early as 2011.

Now a redacted pathology report from the autopsy on Williams' body has been made public and mentions "Diffuse Lewy body dementia,". Given that Dementia with Lewy Bodies can involve vivid visual hallucinations, it has now been speculated that perhaps such hallucinations may have lead to Williams' death.

Media reports, quoting anonymous "family sources," state that Williams' family believes that Lewy body disease was a critical "triggering" factor in his suicide. If so, this would be an unusual manifestation of the disease. Suicides have not been linked specifically to the hallucinations of Lewy Body Disease in the past.

Dennis Dickson, MD

"The use of the term dementia in the neuropathology report should not be inferred to mean that dementia was observed during life," warns Dennis Dickson of the Mayo Clinic in Jacksonville, who says he reviewed the neuropathology report.

"Mr. Williams was given a clinical diagnosis of (Parkinson's) and treated for motor symptoms. The report confirms he experienced depression, anxiety and paranoia, which may occur in either Parkinson's disease or dementia with Lewy bodies," Dickson said.

The asinine reason why the name JCD was converted to CJD

Originally referred to as Jakob-Creutzfeldt disease (and believed by many to rightfully be called simply Jakob's disease), we now refer to this prion disease as Creutzfeldt-Jakob disease. Why? It all stems from a Dr. C. Joseph Gibbs, a colleague of D. Carleton Gajdusek at the National Institutes of Health, who worked on this disease back in the 1960's. Here's the explanation, lifted from Nobel laureate Stanley Prusiner's Madness and Memory: The Discovery of Prions - A New Biological Principle of Disease:

"Alfons Jakob wrote a paper in 1921 describing several cases of progressive dementia with widespread neuronal loss in the brain. A year earlier, Hans Creutzfeldt had described the brain of a woman who died after a prolonged series of seizures. He found widespread vacuolation, but some medical scientists believe that his patient died of a seizure disorder complicated by hypoxic brain damage and doubt that she had what became known as CJD. So why did the named Jakob and Creutzfeldt become flipped in an important report on the disease, regarding the transmission to a chimpanzee? Twenty years passed before I found the answer, in conversation with Gibbs. 'When I was writing my first paper on the transmission of Jakob-Creutzfeldt disease to an ape,' he told me, 'I wanted to rename the disease Gibbs disease. I didn't think this would be acceptable to the scientific and medical communities, so I decided to reverse the names, because my first name is Clarence and my middle name is Joseph and my initials are C.J.' Thus did the diease become known as Creutzfeldt-Jakob disease, or CJD for short - a case of mind-boggling scientific mischief." 

Gibbs (left) and Gajdusek with a New Guinea kuru patient in 1972.

 
A remarkable case of hubris, although from what I hear about Prusiner, he is not one to point fingers at those who grasp credit for the work of others. Gajdusek, also a Nobel prize winner, once wrote in his diary the following about Prusiner:


""I never heard a word of original thought from you nor read such ideas in anything you authored for which I did not recognize immediately its source, which you always went out of your way to obscure. You a heretic? You a martyr? You a defender of unacceptable ideas? Bullshit! You shrewdly jumped onto a bandwagon of creative ideas and experimental work and shrewdly got on to the winning cart, proclaiming outrageously in press and media it was yours! I respect you less and less as your despicable game succeeds and you bask in your coveted fame."

But then again, Gajdusek himself, who died in 2008 at age 85, was no paragon of virtue.In the course of his research trips in the South Pacific to study kuru , Gajdusek had brought 56 mostly male children back to live with him in the United States, and provided them with the opportunity to receive high school and college education. He was later accused by one of these, now an adult man, of molesting him as a child. In fact, seven men testified in confidentiality about Gajdusek having had sex with them when they were boys.  Gajdusek was charged with child molestation in April 1996, based on incriminating entries in his personal diary and statements from a victim. He pleaded guilty in 1997 and, under a plea bargain, was sentenced to 12 months in jail. After his release in 1998, he was permitted to serve his five-year unsupervised probation in Europe. He never returned to the United States and ultimately died in Norway.

Peto's Paradox: why elephants don't get brain cancer

I was recently informed by a second-year medical student that elephants rarely, if ever, get brain cancer -- or other malignancies for that matter. This statement seemed illogical. If every living cell has a chance of becoming cancerous, massive animals like elephants and whales - by virtue of the fact that they have so many more cells -- should have a greater risk of developing cancer than do humans or mice. But, when I looked into it, it turns out that the student was right! A January 2013 article in Nature points out that across species, the occurrence of cancer does not show a correlation with body mass.

The lack of correlation between body mass and cancer risk is known as Peto's Paradox, after epidemiologist Richard Peto of Oxford University in the UK, who noted it in the 1970s. Evolutionary biologists think that it results from larger animals using protective mechanisms that many smaller animals do not.

Evolutionary biologists say that evolution does not always favor tumor-suppressor genes. Although these mechanisms could reduce cancer mortality in any animal, they may come at a cost — reduced fertility, in the case of one research group's model. The result is that for intermediate-sized animals, the evolutionary cost of having many tumor suppressor genes is greater than the benefits of cancer protection they offered. In other words, it is better for the population, evolutionarily, to tolerate more deaths from cancer rather than investing in more costly mechanisms to avoid cancer development. But for massive animals, the cancer avoidance cost of having many tumor suppressor genes is worth it since giant beasts tend to produce few offspring per animal.

Another theory to explain Peto's Paradox is that large animals generate fewer reactive oxygen species resulting from a lower basal metabolic rate and therefore have a lower chance of a suffering a genetic mishap.

Researchers around the world are trying to find the mechanism of Peto's Paradox with hope that it can shed light on cancer prevention and treatment in humans.