Page 221 - Textbook of Pathology, 6th Edition

markers by immunohistochemistry, and by applying image  TABLE 8.3. Five Most Common Primary Cancers in the World. 205
morphometry for cancer cell and nuclear parameters.
Men Women Children (Under 20)
Staging 1. Lung Breast Acute leukaemia
(oral cavity in India) (cervix in India)
The extent of spread of cancers can be assessed by 3 ways— 2. Prostate Lung CNS tumour
by clinical examination, by investigations, and by pathologic 3. Colorectal Colorectal Bone sarcoma CHAPTER 8
examination of the tissue removed. Two important staging 4. Urinary bladder Endometrial Endocrine
systems currently followed are: TNM staging and AJC 5. Lymphoma Lymphoma Soft tissue sarcoma
staging.
TNM staging. (T for primary tumour, N for regional nodal women, and children. As evident from the Table, some types
involvement, and M for distant metastases) was developed of cancers are more common in India while others are
by the UICC (Union Internationale Contre Cancer, Geneva). commoner in the Western populations since etiologic factors
For each of the 3 components namely T, N and M, numbers are different. Neoplasia
are added to indicate the extent of involvement, as under: In general, most common cancers in the developed and
T to T : In situ lesion to largest and most extensive developing countries are as under:
0
4
primary tumour. Developed world: lung, breast, prostate and colorectal.
N to N : No nodal involvement to widespread lymph Developing world: liver, cervical and oesophageal.
About one-third of all cancers worldwide are attributed
3
0
node involvement. to 9 modifiable life-style factors: tobacco use, alcohol
M to M : No metastasis to disseminated haematogenous consumption, obesity, physical inactivity, low fiber diet,
2
0
metastases.
unprotected sex, polluted air, indoor household smoke, and
AJC staging. American Joint Committee staging divides all contaminated injections. Overall, there has been a declining
cancers into stage 0 to IV, and takes into account all the trend in incidence of some of the cancers due to cancer
3 components of the preceding system (primary tumour, screening programmes for cervical, breast, colorectal and
nodal involvement and distant metastases) in each stage. prostate cancer.
TNM and AJC staging systems can be applied for staging
most malignant tumours. EPIDEMIOLOGIC FACTORS
Currently, clinical staging of tumours does not rest on A lot of clinical and experimental research and epidemio-
routine radiography (X-ray, ultrasound) and exploratory logical studies have been carried out in the field of oncology
surgery but more modern techniques are available by which so as to know the possible causes of cancer and mechanisms
it is possible to ‘stage’ a malignant tumour by non-invasive involved in transformation of a normal cell into a neoplastic
techniques. These include use of computed tomography (CT) cell. It is widely known that no single factor is responsible
and magnetic resonance imaging (MRI) scan based on tissue for development of tumours. The role of some factors in
density for locating the local extent of tumour and its spread causation of neoplasia is established while that of others is
to other organs. More recently, availability of positron epidemiological and many others are still unknown.
emission tomography (PET) scan has overcome the limitation Besides the etiologic role of some agents discussed later,
of CT and MRI scan because PET scan facilitates distinction the pattern and incidence of cancer depends upon the
of benign and malignant tumour on the basis of biochemical following:
and molecular processes in tumours. Radioactive tracer A) A large number of predisposing epidemiologic factors or
studies in vivo such as use of iodine isotope 125 bound to cofactors which include a number of endogenous host factors
specific tumour antibodies is another method by which small and exogenous environmental factors.
number of tumour cells in the body can be detected by B) Chronic non-neoplastic (pre-malignant) conditions.
imaging of tracer substance bound to specific tumour antigen. C) Role of hormones in cancer.
A. Predisposing Factors
EPIDEMIOLOGY AND 1. FAMILIAL AND GENETIC FACTORS. It has long been
PREDISPOSITION TO NEOPLASIA suspected that familial predisposition and heredity play a
role in the development of cancers. In general, the risk of
CANCER INCIDENCE developing cancer in relatives of a known cancer patient is
The overall incidence of cancer in a population or a country almost three times higher as compared to control subjects.
is known by registration of all cancer cases (cancer registry) Some of the cancers with familial occurrence are colon, breast,
and by rate of death from cancer. Worldwide, it is estimated ovary, brain and melanoma. Familial cancers occur at a
that about 20% of all deaths are cancer-related; in US, cancer relatively early age, appear at multiple sites and occur in 2
is the second most common cause of deaths, next to heart or more close relatives. The overall estimates suggest that
disease. There have been changing patterns in incidence of genetic cancers comprise not greater than 5% of all cancers.
cancers in both the sexes and in different geographic locations Some of the common examples are as under:
as outlined below. Table 8.3 shows worldwide incidence (in i) Retinoblastoma. About 40% of retinoblastomas are
descending order) of different forms of cancer in men, familial and show an autosomal dominant inheritance.