Chapter 23, Problem 29
Skin cancer carries a lifetime risk nearly equal to that of all other cancers combined. Following is a graph [modified from K. H. Kraemer (1997). Proc. Natl. Acad. Sci. (USA) 94:11–14] depicting the age of onset of skin cancers in patients with or without XP, where the cumulative percentage of skin cancer is plotted against age. The non-XP curve is based on 29,757 cancers surveyed by the National Cancer Institute, and the curve representing those with XP is based on 63 skin cancers from the Xeroderma Pigmentosum Registry.
Provide an overview of the information contained in the graph.
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The table in this problem summarizes some of the data that have been collected on mutations in the BRCA1 tumor-suppressor gene in families with a high incidence of both early-onset breast cancer and ovarian cancer.
Predisposing Mutations in BRCA1
Kindred Codon Nucleotide Coding Effect Frequency in
Change Control
Chromosomes
1901 24 -11 bp Frameshift 0/180
or splice
2082 1313 C→T Gln→Stop 0/170
1910 1756 Extra C Frameshift 0/162
2099 1775 T→G Met→Arg 0/120
2035 NA* ? Loss of NA*
transcript _
Source: (1994). Science 266:66–71. © AAAS.
Examine the types of mutations that are listed in the table, and determine if the BRCA1 gene is likely to be a tumor-suppressor gene or an oncogene.
The table in this problem summarizes some of the data that have been collected on mutations in the BRCA1 tumor-suppressor gene in families with a high incidence of both early-onset breast cancer and ovarian cancer.
Predisposing Mutations in BRCA1
Kindred Codon Nucleotide Coding Effect Frequency in
Change Control
Chromosomes
1901 24 -11 bp Frameshift 0/180
or splice
2082 1313 C→T Gln→Stop 0/170
1910 1756 Extra C Frameshift 0/162
2099 1775 T→G Met→Arg 0/120
2035 NA* ? Loss of NA*
transcript _
Source: (1994). Science 266:66–71. © AAAS.
Although the mutations listed in the table are clearly deleterious and cause breast cancer in women at very young ages, each of the kindred groups had at least one woman who carried the mutation but lived until age 80 without developing cancer. Name at least two different mechanisms (or variables) that could underlie variation in the expression of a mutant phenotype, and propose an explanation for the incomplete penetrance of this mutation. How do these mechanisms or variables relate to this explanation?
Researchers have identified some tumors that have no recurrent mutations or deletions in known oncogenes or tumor-suppressor genes and no detectable epigenetic alterations. However, these tumors often have large chromosomal deletions. What are some possible explanations that could account for the genetic causes behind these tumors?
Skin cancer carries a lifetime risk nearly equal to that of all other cancers combined. Following is a graph [modified from K. H. Kraemer (1997). Proc. Natl. Acad. Sci. (USA) 94:11–14] depicting the age of onset of skin cancers in patients with or without XP, where the cumulative percentage of skin cancer is plotted against age. The non-XP curve is based on 29,757 cancers surveyed by the National Cancer Institute, and the curve representing those with XP is based on 63 skin cancers from the Xeroderma Pigmentosum Registry.
Explain why individuals with XP show such an early age of onset.
Although cancer is not a contagious disease in humans or other vertebrates, there have been rare cases in which cancers have spread from one organism to another. Describe three cases of these contagious cancers and what conditions might have led to their appearance. For an introduction to this topic, see http://www.cancer.org/cancer/cancerbasics/is-cancer-contagious.