Chapter 20

In the following simplified diagram of cell divisions in a multicellular species, the germ-cell and somatic-cell lineages are depicted. Which of the indicated cells (1 or 2) represents the germ line? Write down 1 or 2 as your answer. [Cell Division Graphic]

1

Myelomas are cancers of blood plasma cells—white blood cells that are normally responsible for producing large quantities of antibodies. In the following "Circos plot" for myelomas in a hypothetical mammalian genome, the interchromosomal rearrangements are indicated by red lines and variations in copy numbers are indicated in blue. The positions of named genes are indicated with arrows. On which chromosome do you expect to find the antibody genes? Write down the chromosome number (1 to 5) as your answer.

5

You have analyzed a large set of human cancer-critical genes for a selected group of carcinomas, classifying each of the genes based on whether they are known to undergo somatic or germ-line mutations, as well as based on whether they are dominant or recessive. You then group them and plot the statistics in the following histograms. Which group (a or b) do you think represents somatic, as compared to germ-line, mutations? Which group (1 or 2) do you think represents dominant, as compared to recessive, mutations? (Note that the sum of percentages of somatic and germ-line mutations is more than 100%, since some genes are mutated in both somatic and germ cells). [bar graph: percentage of total genes studied] A. a; 1 B. a; 2 C. b; 1 D. b; 2

A. A;1

Compared to cells of a normal tissue, which of the following occurs less frequently in cells within a solid tumor? A. Apoptosis B. Necrosis C. Cell division D. Mitotic recombination E. Stress

A. Apoptosis

Carcinoma of the uterine cervix in humans ... A. can be largely prevented by vaccination. B. is caused by a retrovirus. C. is caused by activation of a viral Src kinase. D. rapidly progresses (from uterine warts) to malignancy. E. All of the above.

A. Can be largely prevented by vaccination

You have karyotyped cells from two colorectal tumor samples, one from a hereditary nonpolyposis colorectal cancer (HNPCC) patient, and the other from a familial adenomatous polyposis coli (FAP) patient. One group of the karyotypes shows gross chromosomal abnormalities with extra or deleted chromosomes and several translocations and deletions. The other group, however, is almost normal, and comparable to noncancerous samples. Which group would you expect to have loss-of-function mutations in the DNA mismatch repair system genes MSH2 and MLH1 as their primary driver mutations? A. HNPCC, which has an almost normal karyotype B. HNPCC, which has a grossly abnormal karyotype C. FAP, which has an almost normal karyotype D. FAP, which has a grossly abnormal karyotype

A. HNPCC, which has an almost normal karyotype (FAP is way abnormal)

Mutations in two important cancer-critical genes, encoding p53 and Rb, respectively, are commonly found in cancers. What type of mutations are these expected to be? A. Loss-of-function mutations in both genes B. Loss-of-function mutation in p53 and gain-of-function mutation in Rb C. Gain-of-function mutation in p53 and loss-of-function mutation in Rb D. Gain-of-function mutations in both genes

A. Loss-of-function mutations in both genes

Among the following cancers, one is currently leading to the most number of deaths in the United States and in the rest of the world. In the United States, it contributes to cancer mortality more than the next three killing cancers combined. Worldwide, it claims more than 1.5 million lives every year. Which cancer is this? A. Lung cancer B. Breast cancer C. Colon cancer D. Pancreatic cancer E. Stomach cancer

A. Lung cancer

For each of the following genes involved in regulation of cell growth through the mTOR pathway, indicate whether the gene is activated (A) or inactivated (I) in cancer cells compared to normal healthy cells. Your answer would be a four-letter string composed of letters A and I only, e.g. AAAA. ( ) mTOR ( ) Akt ( ) PTEN ( ) PI3K

AAIA

From an immortalized human HeLa cell line with wild-type p53 genes, you have derived a line that lacks both copies of the gene. You then treat the original and derived cells with the anticancer drug doxorubicin, which can activate the p53 pathway in the cell by stalling DNA replication forks and inducing double-strand breaks in DNA. You measure cell proliferation in the presence of different doses of the drug in each of the two cell lines, and plot the results as shown in the graph below. Which cell line (A or B) do you expect to be the original HeLa line? Write down A or B as your answer. [graph: relative cell proliferation]

B

The Ames test is used to test the mutagenicity of a compound suspected to be a carcinogen. In a simple form of the test, the carcinogen is first mixed with a rat liver extract. A disc of filter paper is soaked with this mixture and placed on a culture of a strain of Salmonella typhimurium that is defective in a gene involved in the synthesis of histidine, an amino acid that is essential for cell growth and proliferation. The strain is thus normally unable to grow into visible colonies when the histidine in the culture medium is depleted. In the presence of a mutagen, however, mutations (often "reverse mutations" in the same gene) can enable the bacteria to produce histidine on their own, and therefore grow into colonies. The results of the Ames test for three compounds A, B, and C—each used at the same concentration—are shown in the schematic diagram below. Colonies are indicated with black dots, and the disc is indicated with a white circle at the center of each plate. Which compound (A to C) appears to be a stronger mutagen in this assay? Write down A, B, or C as your answer. [image: three Petri dishes]

B

Which of the molecules (A or B) in the following drawing is a more potent mutagen? Write down A or B as your answer.

B

The genotypes of 400 colorectal cancer tumors are tabulated below, where the number of tumors with or without mutations in each of the two cancer-critical genes, β-catenin and Apc, are indicated. Which row (a or b) corresponds to those with a mutant Apc gene? Which column (1 or 2) corresponds to those with a mutant β-catenin gene? β-catenin 1 2 Apc a. 351 2 b 13 34 A. a; 1 B. a; 2 C. b; 1 D. b; 2

B. A;2

A benign neoplasia of cartilage is called a ... A. Chondrocarcinoma B. Chondroma C. Chondrosarcoma D. Adenochondroma E. Chondromelanoma

B. Chondroma

Which of the following sequential barriers to metastasis is the easiest to overcome for cancer cells in general? A. Vessel entry through acquisition of local invasiveness B. Exit from the blood into a remote tissue or organ C. Survival of cells in the foreign tissue D. Initial growth of cells in the foreign tissue E. Persistence of growth in the remote site

B. Exit from the blood into a remote tissue or organ

The immortalized non-malignant mouse cell line NIH-3T3 was derived from normal mouse fibroblasts in the early 1960s. These cells are able to readily take up exogenous DNA and are prone to transformation by cancer-causing agents, including some retroviruses. DNA extracted from a human bladder carcinoma line is able to transform these cells, as judged by a significant increase in the number of foci (cell clumps) in the cell-culture plates when the DNA is added. The malignant cells contain human DNA, and the DNA can be shown by sequence analysis to contain a single mutant gene that is present in the original bladder carcinoma cell line. The gene codes for a monomeric G protein and was one of the first cancer-critical genes to be identified in this way. The protein encoded by this gene is ... A. Src B. Ras C. Myc D. p53 E. Apc

B. Ras

Retinoblastoma is an early-onset cancer of the retina with a rapid progression, and is mostly diagnosed in children. In its hereditary form, multiple eye tumors usually arise in both eyes, while the nonhereditary form usually causes fewer tumors in only one eye. Treatment may involve a combination of chemotherapy, radiotherapy, and other therapies and the majority of patients can be cured if given the right treatment. However, survivors of one form of retinoblastoma (and not the other form) have a markedly increased frequency of subsequent neoplasms that can lead to other cancers later in life, especially soft-tissue sarcomas. These patients should therefore be closely monitored throughout their lives. Which gene is affected by the primary driver mutation in this cancer as well as the later sarcomas? Which form of retinoblastoma do you think is associated with a higher risk of subsequent neoplasms? A. p53; hereditary B. Rb; hereditary C. Ras; nonhereditary D. p53; nonhereditary E. Rb; nonhereditary

B. Rb; hereditary

According to the cancer stem-cell model for tumor growth and propagation, ... A. transit amplifying cells are incapable of cell division, which is reserved for the cancer stem cells. B. transit amplifying cells constitute the great majority of the cells in the tumor. C. if each stem cell divides to create one stem cell and one transit amplifying cell, the abundance of stem cells in the tumor will increase exponentially over time. D. tumors are genetically heterogeneous, even though they show high phenotypic homogeneity. E. the transit amplifying cells, even though each acts transiently, carry the whole responsibility for maintenance of the tumor in the long term.

B. transit amplifying cells constitute the great majority of the cells in the tumor.

The following simplified diagram shows the typical sequence of genetic changes in a developing colorectal carcinoma. Indicate which event (A to C) corresponds to the following changes. Your answer would be a three-letter string composed of letters A to C only, e.g. CAB. Normal epithelium—(A)—> Early adenomas —(B)—> intermediate and late adenomas—(C)—> Adenocarcinoma and metastases ( ) Activation of K-Ras ( ) Loss of p53 ( ) Loss of Apc

BCA

Three fundamental controls seem to have been subverted in essentially every type of cancer. Choose these three among the following regulatory axes. Your answer would be a three-letter string composed of letters A to F only, in alphabetical order, e.g. BDF. (A) Wnt pathway (B) Rb pathway (C) RTK/Ras/PI3K pathway (D) p53 pathway (E) Hippo pathway (F) GPCR/PKA pathway

BCD

Mutation in which of the following genes is most prevalent in human colorectal cancer cells? A. K-Ras B. β-Catenin C. Apc D. p53 E. MLH

C. Apc

Carcinoma cells that have acquired malignancy and started local invasiveness to begin metastasis ... A. decrease the expression of E-cadherin and undergo mesenchymal-epithelial transition. B. increase the expression of E-cadherin and undergo mesenchymal-epithelial transition. C. decrease the expression of E-cadherin and undergo epithelial-mesenchymal transition. D. increase the expression of E-cadherin and undergo epithelial-mesenchymal transition.

C. Decrease the expression of E-cadherin and undergo epithelial-mesenchymal transition

Once the molecular aberrations in a cancer are understood, drugs can be designed with a rational approach to treat the cancer. Which of the following is NOT true regarding such drugs? A. The drug imatinib (Gleevec®) can inhibit the chimeric tyrosine kinase Bcr-Abl in chronic myelogenous leukemia (CML). B. Even if a protein is not the product of a cancer-critical gene, drugs that specifically block its activity can be effective in curing cancer. C. Imatinib is most effective in treating chronic myelogenous leukemia (CML) in its acute blast-crisis phase. D. Protein kinases have turned out to be relatively easy to inhibit with small molecules. E. The success of imatinib relies on the phenomenon of oncogene dependence in cancer cells.

C. Imatinib is most effective in treating chronic myelogenous leukemia (CML) in its acute blast-crisis phase.

Most DNA tumor viruses inhibit the products of ... A. Apc and Rb B. Brca1 and Rb C. p53 and Rb D. Brca1 and Apc E. Brca1 and p53

C. P53 and Rb

Genetically knocking out both copies of the p53 gene in rats ... A. is embryonic lethal. B. results in a lower malignancy rate, but the rats are otherwise seemingly normal. C. results in a higher rate of cancer onset, but the rats are otherwise seemingly normal. D. increases cell death by apoptosis, leading to developmental defects. E. does not have any effect unless the rats live outside of the laboratory and are exposed to various types of stress.

C. Results in a higher rate of cancer onset, but the rats are otherwise seemingly normal

Which of the following is estimated to be the leading cause of death from cancer in the United States? A. UV light B. Obesity C. Smoking D. Alcohol consumption E. Sedentary lifestyle

C. Smoking

In medical oncology, PET (positron emission tomography) is used to selectively image tumors in the body and to monitor cancer progression and response to treatment. Before performing a PET scan, the patient should fast for at least several hours for blood glucose to be sufficiently low. At the time of the scan, the positron-emitting glucose analog fluorodeoxyglucose (FDG) is injected into the bloodstream and the patient is asked to wait for up to an hour while avoiding physical activity. Finally, the scanner moves slowly over the body to reveal the location of possible tumors. Why do you think the patient should avoid physical activity before the scan? A. To prevent the Warburg effect B. To accelerate glucose uptake by the tumor cells C. To prevent the absorption of the radioactive tracer by healthy tissues D. To promote fermentation in healthy tissues E. All of the above

C. To prevent the absorption of the radioavtive tracer by healthy tissues

Indicate whether each of the following cancers can be best classified as a carcinoma (C), sarcoma (S), or neither of the two (N). Your answer would be a four-letter string composed of letters C, S, and N only, e.g. SSNC. ( ) Breast cancer ( ) Lung cancer ( ) Colorectal cancer ( ) Myeloma

CCCN

Indicate whether each of the following descriptions better applies to a cancer cell (C) or a normal adult cell (N). Your answer would be a four-letter string composed of letters C and N only, e.g. CCNC. ( ) Higher lactate production ( ) Higher oxidative phosphorylation ( ) Contact inhibition ( ) Anchorage independence

CNNC

PARP inhibitors can efficiently kill many breast cancer cells that lack functional Brca1 or Brca2 genes. How do these drugs accomplish this? A. By increasing the ability of p53 in cancer cells to limit cell proliferation B. By inhibiting proteins that are normally inhibited by the Brca1 or Brca2 gene products C. By increasing the occurrences of homologous recombination D. By inhibiting a DNA repair pathway E. By increasing the ability of the cancer cells to repair the mutations in their cancer-critical genes

D. By inhibiting a DNA repair pathway

The effect of the deletion of one copy of the gene encoding p53 is different from the effects caused by other p53 mutations. For example, some loss-of-function mutations in the DNA-binding domain of p53 cripple its function as a transcription regulator. Such a mutation in only one copy of the p53 gene can be enough to confer a p53 loss-of-function phenotype, even when the other copy of the gene on the homologous chromosome is wild type. This is because ... A. p53 is a proto-oncogene. B. these mutations are recessive. C. p53 is a tumor suppressor. D. p53 forms a tetramer. E. p53 can induce apoptosis.

D. P53 forms a tetramer

The requirement for accumulation of multiple mutations in cancer progression is manifested in the normalized percentage of new cases of cancer diagnosed in different age groups. Which of the curves A to E in the following graph better represents the incidence of human cancers as a function of age? [graph: rate of cancer incidence per 100 individuals]

E

You are studying the rising incidence of a certain subtype of cervical cancer in Oceania, and are curious to know whether environmental factors are the dominant cause of the disease. You collect the incidence statistics from indigenous populations as well as from two different immigrant populations in three different countries, as shown in the following table. Do these data appear to be consistent with a dominant role of environmental risk factors (E) or a genetic background (G) for this type of cancer? Write down E or G as your answer. [large table]

E

The Rb gene in retinoblastomas is similar to the Apc gene in polyposis colon carcinomas in that both genes ... A. are tumor suppressors. B. are mutated in one copy in all cells of patients with a hereditary form of the cancer. C. are in a locus that shows loss of heterozygosity in the hereditary form of the cancer. D. should be inactivated in both copies to cause the nonhereditary form of the cancer. E. All of the above.

E. All of the above

Which of the following can lead to p53 stabilization and activation? A. Hypoxia B. Overexpression of Myc C. DNA damage D. Telomere loss E. All of the above

E. All of the above

Which of the following proteins is NOT encoded by a proto-oncogene? A. Src B. Ras C. EGF receptor D. Myc E. E-cadherin

E. E-cadherin

Consider a healthy adult animal in which 1015 cell divisions have taken place since birth. Spontaneous mutations can occur at a rate of approximately one nucleotide out of about ten billion nucleotides every time DNA is replicated. The animal has a diploid genome size of about 2 billion nucleotide pairs. Assuming that only about 5% of mutations occur within genes or gene regulatory sequences, and further assuming that about 0.1% of those may cause cancer, how many potential cancer-causing mutations has the animal been able to successfully suppress (i.e. has been able to survive) during its lifetime? A. Ten thousand B. One hundred thousand C. Ten million D. One billion E. Ten billion

E. Ten billion

Indicate true (T) and false (F) statements below regarding cancer. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) Cancers become less and less heterogeneous as they progress. ( ) Knocking out Ras or Myc genes individually leads to a higher incidence of cancers in mice, and knocking out both genes simultaneously has an even stronger phenotype. ( ) Wnt signaling is important in colon epithelial cells and, correspondingly, mutations in genes in the Wnt pathway are present in most colorectal cancers. ( ) Genome destabilization in a subset of colorectal cancers that have defects in DNA mismatch repair takes the form of chromosome breaks, translocations, and deletions.

FFTF

Indicate true (T) and false (F) statements below regarding cell proliferation in human somatic cancer cells. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) Cancer cells show replicative cell senescence. ( ) Cancer cells maintain their telomeres by inhibiting the enzyme telomerase. ( ) Some cancer cells do not rely on telomerase for telomere lengthening. ( ) Most cancer cells lack telomeres.

FFTF

Indicate true (T) and false (F) statements below regarding the mutational landscape of cancer cells. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) In each cancer, usually there is one driver mutation and a large number of passenger mutations. ( ) It is estimated that about 20% of our genes are cancer-critical. ( ) Cancer-critical genes can encode metabolic enzymes or components of the RNA splicing machinery. ( ) The karyotype is often severely disordered in cancer cells.

FFTT

Indicate true (T) and false (F) statements below regarding colorectal cancers. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) Observation of polyps in the colon epithelium of a patient is an indication of a malignant carcinoma. ( ) Progression of colorectal cancer is very slow and normally takes over 10 years to turn into malignancy. ( ) Colorectal cancers are usually diagnosed later in life. ( ) Invasive colorectal cancer cells usually metastasize to lymph nodes via lymphatic vessels and then into the bloodstream.

FTTT

Indicate whether each of the following descriptions better applies to trastuzumab (T) which targets Her2, imatinib (I) which targets Bcr-Abl, or ipilimumab (P) which targets the CTLA4 protein. Your answer would be a three-letter string composed of letters T, I, and P only, e.g. TTP. ( ) It is NOT an antibody. ( ) It counters the immunosuppressive microenvironment of tumors. ( ) It does not bind to a cancer cell component.

IPP

Indicate whether each of the following viruses is mostly associated with cervical cancer (C), Kaposi's sarcoma (K), liver cancer (L), or stomach cancer (S). Your answer would be a four-letter string composed of letters C, K, L, and S, e.g. CKLS. ( ) Hepatitis-B virus (HBV) ( ) Human immunodeficiency virus (HIV) ( ) Human papillomavirus (HPV) ( ) Helicobacter pylori

LKCS

X-chromosome inactivation in female mammals occurs mostly randomly early in development, resulting in a heterogeneous cell population, with each cell having inactivated one or the other of its X chromosomes and passing on the same X-inactivation choice to its offspring. The inactivated X chromosome is generally hypermethylated and transcriptionally inactive. You are studying a newly discovered type of colon tumor in women that has a morphology distinct from that of other colon adenomas. You extract chromosomal DNA from the tumor cells. You then either keep the DNA untreated, or digest the DNA with a methylation-sensitive restriction enzyme that only cleaves its recognition DNA sequence if the sequence is not methylated. Finally, you amplify by polymerase chain reaction (PCR) a locus on the X chromosome known to be polymorphic in length (i.e. it is expected to be of different sizes in different X chromosomes). The locus has a restriction site for the mentioned enzyme, such that cleavage would prevent PCR amplification. You quantify the amount of PCR products corresponding to shorter and longer versions of the locus, and obtain the results shown in the following table. Do these data appear to be in better agreement with a monoclonal (M) or a polyclonal (P) origin of cancer? A monoclonal origin would mean that all cells in the tumor are the clonal descendants of a single abnormal cell, while a polyclonal tumor is composed of cells from different lineages. Write M or P as your answer.

M

Suppose you are studying tumor heterogeneity in a certain type of melanoma. You have used fluorescence-activated cell sorting (FACS) to specifically isolate those melanoma tumor cells that either do (first category) or do not (second category) express a specific marker present in normal stem cells in the tissue of origin (i.e. the melanocyte stem cells). You implant the same number of cells from each of these categories into severely immunodeficient mice and compare the tumor-formation efficiencies after several weeks, which turn out to be significantly higher for the first category. You then analyze the new tumors using FACS, and find out that the majority of the cells in the tumors that originated from the first category of cells harbor the stem-cell marker, whereas the majority of the cells in the tumors that originated from the second cell category lack the marker, just like their respective founder cells. Do these observations support the existence of cancer stem cells? Write down Yes or No as your answer.

No

The homologous chromosome pairs in our cells do not carry identical sequences in all loci. This heterozygosity (difference between the two copies) can be altered in cancer: in fact, loss of heterozygosity at many loci is observed in cancer cells, through an increase in either homozygosity (two identical copies) or hemizygosity (i.e. loss of one copy). Researchers can take advantage of this loss of heterozygosity in cancer cells to identify genomic loci that contain cancer-critical genes. What type of gene would you expect to find in chromosomal regions with a loss of heterozygosity? Proto-oncogenes (P) or tumor suppressor genes (T)? Write down P or T as your answer.

T

Indicate true (T) and false (F) statements below regarding cancer incidence and cancer prevention. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) Over half of all cancers are preventable by lifestyle changes. ( ) The age-adjusted cancer death rates have increased steadily since 1900, mostly due to the industrial way of life. ( ) Currently, more than half of all cancer patients survive at least five years post-diagnosis. ( ) About half of all cancers are thought to arise by infection with viruses, bacteria, or parasites.

TFTF

Indicate true (T) and false (F) statements below regarding the properties of cancer cells. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) Cancer cells invade and colonize territories that normally belong to other cells. ( ) Unlike in normal tissues, cell death is extremely rare in tumors. ( ) Cancer cells grow and proliferate in defiance of normal restraints. ( ) Malignant tumors are composed of cells that grow and proliferate, but still have not acquired invasiveness.

TFTF

Indicate whether each of the following descriptions better applies to proto-oncogenes (P) or tumor suppressor genes (T). Your answer would be a four-letter string composed of letters P and T only, e.g. PPPT. ( ) Cancer mutations in these genes are usually recessive. ( ) Cancer mutations in these genes include gene duplications. ( ) Cancer mutations in these genes are responsible for most hereditary cancers. ( ) Cancer mutations in these genes are commonly in the form of nonsense (truncating) mutations that abort protein synthesis.

TPTT

Indicate true (T) and false (F) statements below regarding cancer. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) Cancer can be induced by infectious agents such as viruses. ( ) The earlier a cancer is diagnosed, the better the chances are for a cure. ( ) Most cancers originate from a single aberrant cell. ( ) A single mutation is NOT enough to turn a normal cell into a cancer cell.

TTTT