Chapter 081. Principles of Cancer Treatment (Part 2) ppsx

Chapter 081. Principles of
Cancer Treatment
(Part 2)
Figure 81-1


Gompertzian tumor growth.
The growth fraction of a tumor declines exponentially over time (top). The
growth rate of a tumor peaks before it is clinically detectable (middle). Tumor size
increases slowly, goes through an exponential phase, and slows again as the tumor
reaches the size at which limitation of nutrients or auto- or host regulatory
influences can occur.
The maximum growth rate occurs at 1/e, the point at which the tumor is
about 37% of its maximum size (marked with an X). Tumor becomes detectable at
a burden of about 10
9
(1 cm
3
) cells and kills the patient at a tumor cell burden of
about 10
12
(1 kg). Efforts to treat the tumor and reduce its size can result in an
increase in the growth fraction and an increase in growth rate.
Principles of Cancer Surgery
Surgery is used in cancer prevention, diagnosis, staging, treatment (for both
localized and metastatic disease), palliation, and rehabilitation.
Prophylaxis
Cancer can be prevented by surgery in people who have premalignant
lesions resected (e.g., premalignant lesions of skin, colon, cervix) and in those
who are at increased risk of cancer from either an underlying disease (colectomy
in those with pancolonic involvement with ulcerative colitis), the presence of

genetic lesions (colectomy for familial polyposis, thyroidectomy for multiple
endocrine neoplasia type 2, bilateral mastectomy or oophorectomy for familial
breast or ovarian cancer syndromes), or a developmental anomaly (orchiectomy in
those with an undescended testis). In some cases, prophylactic surgery is more
radical than the surgical procedures used to treat the cancer after it develops. The
assessment of risk involves many factors and should be undertaken with care
before advising a patient to undergo such a major procedure. For breast cancer
prevention, many experts use a 20% risk of developing breast cancer over the next
5 years as a threshold. However, patient fears play a major role in defining
candidates for cancer prevention surgery. Counseling and education may not be
enough to allay the fears of someone who has lost close family members to a
malignancy.
Diagnosis
The underlying principle in cancer diagnosis is to obtain as much tissue as
safely possible. Owing to tumor heterogeneity, pathologists are better able to make
the diagnosis when they have more tissue to examine. In addition to light-
microscopic inspection of a tumor for pattern of growth, degree of cellular atypia,
invasiveness, and morphologic features that aid in the differential diagnosis,
sufficient tissue is of value in searching for genetic abnormalities and protein
expression patterns, such as hormone receptor expression in breast cancers, that
may aid in differential diagnosis or provide information about prognosis or likely
response to treatment. Histologically similar tumors may have very different gene
expression patterns when assessed by such techniques as microarray analysis using
gene chips, with important differences in response to treatment. Such testing
requires that the tissue be handled properly (e.g., immunologic detection of
proteins is more effective in fresh-frozen tissue rather than in formalin-fixed
tissue). Coordination among the surgeon, pathologist, and primary care physician
is essential to ensure that the amount of information learned from the biopsy
material is maximized.
These goals are best met by an excisional biopsy in which the entire tumor

mass is removed with a small margin of normal tissue surrounding it. If an
excisional biopsy cannot be performed, incisional biopsy is the procedure of
second choice. A wedge of tissue is removed, and an effort is made to include the
majority of the cross-sectional diameter of the tumor in the biopsy to minimize
sampling error. The biopsy techniques that involve cutting into tumor carry with
them a risk of facilitating the spread of the tumor. Core-needle biopsy usually
obtains considerably less tissue, but this procedure often provides enough
information to plan a definitive surgical procedure. Fine-needle aspiration
generally obtains only a suspension of cells from within a mass. This procedure is
minimally invasive, and if positive for cancer it may allow inception of systemic
treatment when metastatic disease is evident, or it can provide a basis for planning
a more meticulous and extensive surgical procedure.