Chapter 081. Principles of Cancer Treatment (Part 2)

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 109 (1 cm3) cells and kills the patient at a tumor...
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Chapter 081. Principles of Cancer Treatment (Part 2) 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). Thegrowth rate of a tumor peaks before it is clinically detectable (middle). Tumor sizeincreases slowly, goes through an exponential phase, and slows again as the tumorreaches the size at which limitation of nutrients or auto- or host regulatoryinfluences can occur. The maximum growth rate occurs at 1/e, the point at which the tumor isabout 37% of its maximum size (marked with an X). Tumor becomes detectable ata burden of about 109 (1 cm3) cells and kills the patient at a tumor cell burden ofabout 1012 (1 kg). Efforts to treat the tumor and reduce its size can result in anincrease in the growth fraction and an increase in growth rate. Principles of Cancer Surgery Surgery is used in cancer prevention, diagnosis, staging, treatment (for bothlocalized and metastatic disease), palliation, and rehabilitation. Prophylaxis Cancer can be prevented by surgery in people who have premalignantlesions resected (e.g., premalignant lesions of skin, colon, cervix) and in thosewho are at increased risk of cancer from either an underlying disease (colectomyin those with pancolonic involvement with ulcerative colitis), the presence ofgenetic lesions (colectomy for familial polyposis, thyroidectomy for multipleendocrine neoplasia type 2, bilateral mastectomy or oophorectomy for familialbreast or ovarian cancer syndromes), or a developmental anomaly (orchiectomy inthose with an undescended testis). In some cases, prophylactic surgery is moreradical than the surgical procedures used to treat the cancer after it develops. Theassessment of risk involves many factors and should be undertaken with carebefore advising a patient to undergo such a major procedure. For breast cancerprevention, many experts use a 20% risk of developing breast cancer over the next5 years as a threshold. However, patient fears play a major role in definingcandidates for cancer prevention surgery. Counseling and education may not beenough to allay the fears of someone who has lost close family members to amalignancy. Diagnosis The underlying principle in cancer diagnosis is to obtain as much tissue assafely possible. Owing to tumor heterogeneity, pathologists are better able to makethe 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 proteinexpression patterns, such as hormone receptor expression in breast cancers, thatmay aid in differential diagnosis or provide information about prognosis or likelyresponse to treatment. Histologically similar tumors may have very different geneexpression patterns when assessed by such techniques as microarray analysis usinggene chips, with important differences in response to treatment. Such testingrequires that the tissue be handled properly (e.g., immunologic detection ofproteins is more effective in fresh-frozen tissue rather than in formalin-fixedtissue). Coordination among the surgeon, pathologist, and primary care physicianis essential to ensure that the amount of information learned from the biopsymaterial is maximized. These goals are best met by an excisional biopsy in which the entire tumormass is removed with a small margin of normal tissue surrounding it. If anexcisional biopsy cannot be performed, incisional biopsy is the procedure ofsecond choice. A wedge of tissue is removed, and an effort is made to include themajority of the cross-sectional diameter of the tumor in the biopsy to minimizesampling error. The biopsy techniques that involve cutting into tumor carry withthem a risk of facilitating the spread of the tumor. Core-needle biopsy usuallyobtains considerably less tissue, but this procedure often provides enoughinformation to plan a definitive surgical procedure. Fine-needle aspirationgenerally obtains only a suspension of cells from within a mass. This procedure isminimally invasive, and if positive for cancer it may allow inception of systemictreatment when metastatic disease is evident, or it can provide a basis for planninga more meticulous and extensive surgical procedure.