Tumor Bio 336 Midterms and Quizzes

Choose two types of cancers from this chart where there are clear differences in the incidence rates between developed and developing countries and provide a reasonable explanation for these differences.

"Cervical cancer" : access to health care in the form of pap smears makes "cervical cancer" a controllable disease in US/western Europe. Stomach cancer: Chronic Helicobacter pylori infections in underdeveloped parts of the world are strongly correlated with high stomach cancer rates Liver cancer: High Hepatitis B and C virus infection rates in underveloped parts of the world. Colon, breast cancer: obesity, dietary factors, sedentary life style in developed countries contributes

The Ras oncogene was discovered independently as an oncogene in a murine retrovirus. Ras is a 21 kiladalton (kDa) protein. Approximately what size (in base pairs) do you think the Ras gene was in the oncogenic retrovirus?

21 kD is 21,000 daltons. Average MW of the 20 amino acids is ~115 daltons. Therefore the Ras protein is composed of approximately 182 amino acids. Since each of the 182 codons is composed of 3 nucleotides, the Ras ORF in the virus must be approximately 546 base pairs.

Barretts Esophagous is not considered a neoplasm. How would you classify it? Is it a risk factor for developing into a neoplasm?

A metaplasia. And, yes, it is a risk factor for carcinoma of the esophagus.

Therapeutic approach for a mutation in the intracellular domain of an RTK that results in the activation of kinase activity even in the absence of dimerization

A small molecule inhibitor that acts at the (intracellular) active-site of the enzyme

Malignant cells will sometimes show clear signs of abnormal mitosis. What is the most likely cause of this?

Abnormal mitoses are usually a result of an abnormal karyotype - aneuploidy. An incorrect number of chromosomes and/or chromosomes with more than a single centromere. Abnormal karyotypes are generally associated with malignant tumors.

Therapeutic approach for a tumor expressing HER2

Antibody against HER2 that prevents dimerization

Therapeutic approach for an overexpressed ligand of an RTK

Antibody that binds the ligand

The "Ames Test" was important because it solidified the notion that many carcinogens are mutagens. However,the test, itself, has important limitations when it comes to identifying human carcinogens. Give two examples where a known human carcinogen would fail to score positive in the test, and explain why.

Asbestos is a chemically inert fiber that is not internalized into cells; it would not score positive as a mutagen. While the "modified" Ames test attempts to account for conversion of non-mutagenic compounds into reactive compounds by the inclusion of liver enzymes, it is very possible that some carcinogens would still be missed in the assay. Inert implanted objects that induce sarcomas when in rodents (see lecture notes) Clearly microbes/viruses associated with human cancer would not score positive

Why is chemotherapy, rather than radiation, the most common approach to therapy if metastases are suspected?

Because chemotherapeutics are delivered systemically and are able to hit potenitial micrometastases that cannot be visualized. It would be impractical and unwise to use whole-body radiation as a means of targeting unseen micrometastases

Histologically, cells of the tumor appear similar to normal cells of that tissue.

Benign

Give one example where a benign tumor might prove lethal.

Benign brain tumor, due to pressure on healthy tissues of brain Benign tumor of pancreas that might secrete lethal levels of insulin; Benign tumor of adrenal gland secreting lethal levels of epinephrine

Give two examples where a "benign" tumor might be lethal.

Benign tumor of the brain - physical constraints of the skull can cause damage to other parts of the brain as the tumor expands. Benign tumor of adrenal gland or pancreas can secrete lethal levels of epinephrine or insulin, respectively.

Why does limited blood supply to a tumor limit the effectiveness of both chemotherapy and radiation therapy?

Blood supply is obviously needed to deliver drugs to the tumor; poor blood supply, poor delivery. Since radiation therapy works by generating oxygen radicals, radiation therapy is also dependent on blood supply (low bloow perfusion, poor oxygen delivery).

The tumor is supported by a robust blood supply

Both malignant and benign; NOT a defining characteristic

Matrix Metalloproteinases (MMPs) play an important role in breakdown of the basement membrane, a critical step in the metastatic cascade. Give two additional functions for MMPs in the metastatic cascade.

Breakdown of junctions that hold epithelial cells to one another. Liberation of latent growth factors and/or pro-angiogenic factors that are sequestered in the extracellular space. Breakdown of extracellular matrix can create space for tumor cell to migrate and for endothelial cells to expand to create new capillaries.

N-nitrosodimethylamine on the "Ames test"

Can chemically modify DNA and lead to mutations

For each of your answers in part a, explain why there is a difference in cancer rates between developed and developing countries (or just state that there is no difference, if thats the case).

Cervical cancer: lack of access to regular pap screening in developing countries Stomach cancer: clear water and sanitation problems in developing countries is associated with higher rates of chronic H. pylori infections Hepatitis B virus: endemic in certain parts of the world. Contaminated blood supplies and lack of use of the vaccine are contributing factors.

Why is chemotherapy, rather than radiation therapy, the most common approach to therapy if metastases are suspected?

Chemotherapy is generally systemic and therefore more likely to target micrometastases, which will usually be undetectable.

Name TWO types of cancers shown on the figure where behavioral factors are thought to play a causative role in the disease and state the behavior factors.

Colon cancer, breast cancer Lung- Smoking

One good example of a type of cancer that has been epidemiologically linked to obesity

Colon cancer, breast cancer, kidney, pancreatic, esophageal, and others (see slide 37 of edpidemiology lecture)

State two important general and/or experimental observations that support the idea that carcinogenesis is a multi-step process.

Correlation of pathologic intermediates in 'colon cancer' with specific genetic alterations Age-dependency Retention of 8:21 chromosomal translocation in stem cells of "cured" AML patients Time between exposure to carcinogens and development of cancer

In almost all cases of surgical removal of a tumor, the tumor tissue will be sent to the pathologist. Give four characteristics that the pathologist might be looking at to make the distinction between a benign and malignant tumor.

Differentiation state of the cells (less differentiation assoc. with malignantic tumor) Increased mitotic activity associated with malignant tumor Evidence of abnormal mitotic activity (charac. of malignant tumor) The nucleus to cytoplasm ratio (i.e., the size of the nuclei; larger assoc. with malig.) Expression of specific malignancy-associated markers (e.g., over expression of a specific cancer-associated protein)

For a breast cancer patient, give two criteria a patient being a good candidate for a sentinel lymph node biopsy.

Early stage tumor Young patient First time cancer patient (i.e., not a recurrence

Give TWO examples of how stromal cells of a tumor can support the growth or metastasis of the parenchymal cells of a tumor.

Endothelial cells provide blood vessels/blood supply Stromal cells can be a source of growth factors Stromal cells can be a source of extracellular proteases that promote several steps of the metastatic cascade (see question 8)

Sentinel Lymph Node biopsy is often performed for breast cancer patients. Describe a good candidate for thisprocedure and a bad candidate for this procedure.

Good candidate: younger woman, smaller tumor, first-time breast cancer patient Bad candidate: older woman, recurrent breast cancer patient, or obvious metastases at other sites at time of diagnosis

You were telling your friend about oncogenic retroviruses, and your friend guessed that HIV-1 must be an oncogenic retrovirus because they've read that AIDS patients frequently develop Kaposi's sarcoma. You correct your friend by saying...

HIV causes immunosuppression, which makes patients susceptible to many other viruses and microbes, including human herpes virus 8 (HHV8). It is the HHV8 that plays a causative role in Kaposi's sarcoma, not HIV. So the oncogenic effects of HIV are indirect.

Sometimes a surgeon might be able to easily distinguish a benign tumor from a malignant tumor. State two characteristics that might allow a surgeon to make the distinction.

Highly circumscribed/encapsulated tumor would suggest a benign tumor Lack of defined borders between tumor and normal tissue with clear signs of tissue invasion would indicate malignancy. Abnormal appearance of nearby lymph nodes might suggest malignancy. Evidence of some normal aspect of tissue behavior might suggest benign (example: benign liver tumor secreting bile)

Propose two enzymes or proteins that might be attractive drug targets in leukemias that express the Tax protein of HTLV-1.

IKK the kinase for IkB. If IKK could be inhibited, would IkB never be phosphorylated and it would not be degraded and therefore NFkB would not be activated. Inhibition of the ubiquitination or degradation of IkB, either at the level of the E3 enzyme or the proteasome.

A younger woman with early stage breast cancer undergoes a Sentinel Lymph Node biopsy and the sentinel node is found to contain cancer cells. Briefly describe some immediate follow-up work that is likely to be done, and how the results of these further tests might affect treatment.

If the sentinel node was positive, additional nodes would also be removed and examined. If cancer was found disseminated throughout the lymph nodes, this would increase the probability that the cancer has already spread elsewhere in the body. Together, this would likely lead to more aggressive chemotherapy.

In defining their six "hallmarks of cancer", Hanahan and Weinberg refer to genomic instability as an "enabling characteristic". Explain what this means.

If there were not for an overlying genomic instability associated with the process of carcinogenesis, the mutations leading to acquisition of the six hallmarks of cancer would likely never occur. In other words, cancer should theoretically never occur given the low mutation rate of normal human cells.

How does the cancer stem cell theory influence our evaluation and/or identification of effective cancer therapies?

If we select drugs simply based on their ability to shrink the tumor we may be missing the small cancer stem cell population, making recurrence a strong likelihood.

The single distinguishing characteristic between carcinoma and carcinoma in situ is.

Invasion. With CIS there is no evidence of invasion through the basement membrane.

The linkage between two ubiquitin molecules in a polyubiquitin chain

Isopeptide bond (amide/peptide bond)

For most types of cancer, what are two important reasons why it is difficult to address the question of whether tissue stem cells were the target or initiating cell in carcinogenesis?

It is still difficult to even identify stem cells for most tissue types Even if you can identify them, it is very difficult to identify systems where you can track the cell lineage of cancer, particularly given the time scale of cancer development.

The idea that cancers contain a stem cell population has been around for a long time, long before we had an understanding of how to identify or characterize stem cells. Why did the idea make sense?

It made sense because if cancer is a time-dependent multi-step process, then the cell in which the first genetic alteration took place must stick around for a long time before the 1st events occur. If the cell in which the 1st event occurred was simply lost over a relatively short time period, then cancer would never happen. More recently, we know that cell regulatory pathways that control stem cell behavior also can be involved in cancer cell regulation (e.g., Wnt pathway, Sonic hedgehog, Notch pathways).

Imagine you are taking this course 50 years in the future Predict TWO significant differences that you would be likely to see in an updated version of this figure.

Lung cancer rates will likely to significantly less in developed countries; the lag in smoking rates in developing countries is likely to be followed by a lag in lowering of smoking rates HPV vaccines introduced worldwide will likely result in a dramatic drop in cervical cancer everywhere. Colon cancer rates in developed countries, and hopefully worldwide, will decrease, and people realize the connection between diet/obesity with this and other types of cancers.

Abnormal mitotic figures are seen on histological slices

Malignant

Cells of the tumor are highly aneuploid

Malignant

Histologically, cells of the tumor appear very undifferentiated

Malignant

More likely to be anaplastic

Malignant

To the surgeon, the margins of the tumor are difficult to discern.

Malignant

Tumor cells are detected in nearby lymph nodes

Malignant

Tumor cells have broken through the basement membrane

Malignant

Is "Barrett's Esophagus" best described as a dysplasia, metaplasia, or hyperplasia?

Metaplasia

Where do most "transformed" human cell lines come from?

Most transformed cells lines are derived from malignant tumors (e.g., HeLa cells were derived from a cervical cancer; Saos2 cells were derived from an osteosarcoma). It is also possible to generate transformed cells in culture by expression of specific combinations of oncogenes.

The tumor contains a stem cell population

NOT a defining characteristic

The tumor is very large (>10^12 cells)

NOT a defining characteristic

Cells of the tumor contain a stem cell population

NOT a defining characteritic

A mutation of polyoma middle T antigen that eliminates PP2A binding

NOT oncogenic

A mutation that prevents localization of an RTK to the plasma membrane

NOT oncogenic

Alteration of a major auto-phosphorylation site of an RTK from tyrosine to alanine

NOT oncogenic

Bruce Ames and the Ames Test

Nearly all carcinogens (as identified by epidemiologists) are mutagens

Cells are metaplastic

Neither malignant nor benign

No stromal cells are present

Neither malignant nor benign

Very rapid tumor growth

Neither malignant nor benign; NOT a defining characteristic

Asbestos on the "Ames test"

No, Asbestos is chemically inert and would not even enter Salmonella cells. It doesnt enter human cells, either, even when it is acting as a carcinogen.

one good mechanistic explanation for how obesity may be linked to cancer progression

Obesity can lead to insulin resistance and chronically elevated levels of insulin; this can in turn lead signal release of sequestered IGF1 (insulin-like growth factor 1). Both insulin and signal ISG1 through their receptors, leading to either suppression of apoptosis (a hallmark of cancer) or cellular proliferation.

A metastatic tumor that was seeded by a single cell might be expected to be homogenous (i.e., all cells of the tumor are identical), but this is very often not the case. Explain why cells of the metastatic tumor might not be genetically or morphologically identical.

On-going genetic selection and mutations can create genetically heterogenous field of cells Differentiation of cells derived from the initial metastatic cell can create a field of cells that appear heterogenous (even if they are genetically identical)

Let's say a patient has a metastatic tumor that was seeded by exactly 1 malignant tumor cell, yet the metastatic tumor appears to be composed of heterogeneous cell types. Give two possible explanations that might account for the heterogeneity of the tumor.

On-going mutations occurring in cells derived from the initial seed cell Differentiation of cells from derived initial seed cell Recruitment of stromal cells might also contribute to heterogeneous population of cells at site of metastasis.

A mutation that deletes extracellular domain of an RTK

Oncogenic

A mutation that deletes the CT 10 amino acids of Src

Oncogenic

Inactivating mutations in both alleles encoding the SHP1 phosphatase

Oncogenic

Inactivating mutations of both alleles of the Socs-1 gene

Oncogenic

A mutation that results in overexpression of a ligand of a receptor tyrosine kinase (RTK).

Oncogenic. Autocrine expression of an RTK ligand could lead to constitutively on signaling.

Perhaps the clearest indicator that the Warburg Effect is a true and real characteristic of cancer cells is that it is the basis for imaging tumors by Positron Emission Tomography (i.e., PET scans). Briefly describe how the Warburg effect is related to the PET scan.

PET scans detect cells that have preferentially taken up fluorodeoxyglucose (FDG). Glucose flux is greater in cells that are undergoing glycolysis rather than the TCA cycle, so these cells will take up more FDG. According to Warburg, cancer cells continue to undergo gylcolysis even under well-oxygenated conditions, and therefore almost always have a greater glucose flux than surrounding normal cells.

A tyrosine residue and a phosphotyrosine residue

PO3 attached to OH group on the benzene ring of tyrosine

The single major factor responsible for the current low rate of uterine cervical cancer rates in the USA is the

Pap smear.

Is Barrett's Esophagus a neoplasia, a potential precursor to neoplasia, or neither?

Precursor to neoplasia

Percival Pott and his chimney sweeps

Prolonged/chronic exposure to certain chemicals can lead to cancer (not unlike what Yamagiwa discovered in the laboratory over 100 years later)

Your friend has a cat infected with FLV (feline leukemia retrovirus). Knowing that you are taking Bio 336, your friend asks you whether retroviruses are a major cause of human cancer and/or whether they are ever associated with human cancers. You provide your friend with the following succinct but comprehensive answer to this question:

Retroviruses are certainly not a major cause of human cancer. The one clear link, however, is HTLV-1 and its association with T cell leukemia. HTLV-1 does not encode a viral version of a cellular proto-oncogene; rather it expresses a viral protein that influences T cell proliferation (Tax). An important final point is that while retroviruses are not a significant cause of human cancer, studying retroviruses in diverse animals (birds, mice, and others) has led to important insights into the genes and proteins involved in human cancer.

The SH2 domain of Src

SH2 domains bind phosphotyrosine-containing proteins. They are found not only in Src, but many other signaling pathways related to receptor tyrosine kinases.

The SH3 domain of Src

SH3 domains bind to proline-containing peptides (e.g., PPLP). In Src, this binds to the linker region, keeping the Src in an inactive state. PPLP sequences in other proteins can compete for binding to the Src SH3 domain, which pushes Src into its kinase-active state. SH3 domains are also found in many other signaling proteins.

What is the rationale behind the use of "Sentinal Node" biopsies? (don't tell me how this is done, tell me why it is done)

SLN biopsies are used for early stage cancer to increase likelihood of detection of lymph node metastases.By identifying the most likely nodes to which cancer cells might be migrating, the pathologist can concentrate on detecting metastases here. If the SLN is negative, this would suggest primary tumor has not yet metastasized, sparing additional nodes. If SLN is positive, treatment options must be weighed according to many factors. Importantly, the procedure is a biopsy procedure, not a treatment. The SLN is not removed with the any firm conviction that this would stop the spread of the cancer. If the SLN is positive, other nodes may also be positive and it may have spread beyond the nodes to other tissues.

draw a chemical structure that is representative of such a modification with as much detail as possible (e.g., amino acid structure + modification)

See lecture notes for structures (for example, slide 15 of lecture 9 shows the structure of phosphotyrosine)

Examples of contralateral metastases are when a breast carcinoma metastasizes, for example, from one breast to the other or from one kidney to the other. Which of the two main hypotheses to account for the patterns of tumor metastasis would best account for contralateral metastases (explain)?

Seed-soil. Circulation patterns would not favor transport of cell from one kidney to another; they would encounter other capillary beds before seeing the other kidney. On the other hand, if the cells were only capable of growing in the original environment that they developed, then contralateral tumors might be the only type that are seen, even if they occur at a low frequency.

An important event in characterization of Rous Sarcoma Virus was the isolation of RSV mutants that were competent for replication but defective for transformation. These RSV derivatives had acquired mutations in which gene?

Src! A mutation, for example, that killed the kinase activity of Src would result in a virus that would not transform (but it would still be able to replicate).

In terms of classifying and describing a tumor, what does "Stage 4" mean?

Stage 4 implies clear evidence of distant metastases. This is obviously as bad as it gets for any specific type of cancer.

Name TWO types of cancers shown on the figure where a virus or a microbe is thought to play a causative role in the disease, and name the infectious agents.

Stomach cancer (Helicobacter pylori) Uterine cervical cancer (HPVs) Liver cancer (Hepatitis B and C viruses)

Regardless of whether cancer initiates in the stem cells of a given tissue, there is evidence consistent with the idea that cancers have a population of stem cell-like cells (cancer stem cells). Describe one of these lines of evidence.

The "colon cancer", breast cancer, or AML studies, where a small sub-population of very undifferentiated (stem cell-like) cells could efficiently reconstitute the original tumor in immunocompromised mice, while the bulk of more differentiated tumor cells could not.

Name two characteristics of the CC-IC population that were consistent with the idea that these were "cancer stem cells" (i.e., played the equivalent role in cancer as normal tissue stem cells play in maintenance of normal tissues) .

The CC-IC population represented a very small fraction of the total tumor cell cells. Like stem cells, the CC-IC was able to recapitulate the original tumor in all of its complexity. The CC-IC could be re-isolated from the experimentally re-seeded tumor, and used to seed the tumor yet again, recapitulating with each iteration the original tumor.

What are two features that distinguish a transformed cell line from an immortalized cell line?

The ability of transformed cells to induce tumor formation in an immunodeficient mouse Immortalized cells are generally "contact inhibited" (i.e., they stop growing when cells are all touching one another) Transformed cells will generally grow in soft agar (i.e., they don't require a physical support surface)

There are two ATP-dependent steps in ubiquitin-dependent Which proteolysis. proteins in this system consume ATP, and what is the energy of ATP being used for?

The activation of ubiquitin by the E1 enzyme consumes a molecule of ATP in making ubiquitin-AMP. Ub-AMP then reacts with the active site cysteine of the enzyme to form a Ub-thioester bond. The proteasome uses ATP to unfold substrate proteins so that they can enter the proteasome via the narrow channel at either end of the core particle.

Give two lines of evidence that support the idea that carcinogenesis is a multi-step process.

The association of specific genetic alterations with pathologic intermediates in the development of colon cancer The existence of cancer-prone families The strong age-dependence for most types of cancer The generally period of time of exposure to known carcinogens and the appearance of cancer

The SH1 domain of Src

The catalytic domain of Src; it catalyzes tyrosine phosphorylation of itself and other signaling proteins.

An epoxide derivate of benzo[a]pyrene on the "Ames test"

The epoxide form is highly reactive and can modify DNA

Consider the "seed-soil" model for explaining the metastasis of malignant cells. What might be in the "soil" that makes it hospitable for the circulating tumor cells?

The expression of growth factors or cytokines at the second site can greatly influence the growth of tumor cells.

In terms of cancer treatment, describe the importance of determining the identity of the CC-IC population.

The importance is that if you know what the characteristics of the CC-IC and can track it, then therapies can be designed that specifically target the CC-IC. If you don't target the CC-IC (but simply reduce the mass of the tumor would killing the CC-IC) the tumor will always have the possibility of recurring.

Consider the Romanian woman with the 175 pound benign tumor. Give one good reason why surgeons were hesitant to surgically remove the tumor once it became very large.

The incredible network of blood vessels that were serving the tumor tissue would make it difficult to remove (i.e., high risk of bleeding to death).

What is a sentinel lymph node?

The sentinel node is that node that receives draining lymph fluid from the site of a tumor. It is NOT the "closest" lymph node to the tumor; if finding the closest lymph node was the objective they would just use a ruler.

Paget and the metastasis of cancers

The spread of cancers is not random. Certain types of cancers have a tendency to metastasize to certain other sites. Paget favored the seed-soil model.

A "contralateral" metastasis is when a carcinoma metastasizes, for example, from one breast to the other or from one kidney to the other. State (very briefly) the two central hypotheses to account for the patterns of tumor metastasis, and state which of these would best account for contralateral metastases.

The two hypotheses are that circulatory patterns (blood and lymph fluid) determine pattern of metastases, and the seed-soil hypothesis, which states that dispersed cells are likely to take survive and proliferate at the most hospitable sites. The seed-soil hypothesis best accounts for contralateral tumors since the circulation of blood from one kidney to the other, or from one breast to the other, is not direct. Therefore, for a tumor to have metastasize in this manner strongly suggests that there was something unique about the environment in which the primary tumor developed that allowed the disseminated tumor cells to take hold only in that environment.

Give to good reasons why it is important to understand the mechanism of chemotherapeutic drugs when using them in combination.

To combat drug resistance To use drugs that kill cells at different phases of the cell cycle, increasing the chance of potential cell killing during the time-frame of treatment.

A pathology report describes a tumor as adenocarcinoma in situ. List three things you can discern from this description.

Tumor cells are classified as malignant based on pathology There is no evidence for invasion. Tumor cells are derived from glandular epithelium Other general descriptions of malignant cells were acceptable or partially acceptable (e.g., undifferentiated appearance)

UV irradiation on the "Ames test"

UV irradiation leads to DNA damage (crosslinks) and mutations

name a specific protein that is subject to this type of modification/regulation.

Ubiquitination - IkB; phosphorylation - Src, receptor tyrosine kinases, IkB; lipidation - Src

State one example of a type of post-translational modification that we've talked about so far in class.

We've talked about phosphorylation, ubiquitination, lipidation (myristilation of Src), and proteases.

We now know that there are two general classes of oncogenes: dominant oncogenes and recessive oncogenes (i.e., tumor suppressors). Bob Weinberg's approach for isolating an oncogene from a bladder carcinoma cell line could only have identified one of these. Which one? Explain your answer.

Weinberg's approach could only have identified dominant oncogenes. He was putting an extra copy of a gene into a cell that presumably had two wild-type alleles to begin with; if that resulted in transformation it would be, by definition, a dominant oncogene.

Tumorigenic retroviruses have been identified in animals. State three different mechanisms by which retroviruses have been shown to promote tumorigenesis.

a. Retroviruses, analogous to Rous Sarcoma Virus, can end a viral oncogene that is a derivative of a host gene (as in v-Src for RSV) b. Retroviruses can insert themselves either upstream or downstream of a cellular proto-oncogene in such a way that either a viral enhancer or promoter is used drive overexpression of oncogene. c. Retroviruses can encode viral regulatory proteins that influence cellular signaling pathways, as in the case of HTLV-1 expressing the viral Tat protein.

f) (4) What are two experimental ways to distinguish immortalized from transformed cells?

growth in softer agar (i.e., anchorage-independent growth) ability to form tumors in immunosuppressed mice