Colorectal Cancers, Screening
in the General Population: Focusing
Type of article: Review
Boumediene Elhabachi; Mama Sidelmrabet Ben Brahim
Faculty of medicine University of Sidi
Bel Abbes, Algeria
CHU Dr Hassani
A.E.K, Algeria
Colorectal cancers are common throughout the world,
although their incidence varies across continents and countries. 28% of these
cancers are rectal and two-thirds of the remaining 72% are of left colonic
location. Screening and prevention have proven effective in reducing the
incidence of these cancers and their mortality. The best screening results in
the so-called average-risk general population have been obtained in the USA,
where first-line endoscopy is the gold standard when in other countries,
especially European ones; screening was done by the search for occult blood in
the stool. This group, however, became heterogeneous due to the intervention of
environmental factors and co-morbidities; a colonoscopy is then proposed to
those subjects considered at average risk. Virtual colonoscopy has excellent
sensitivity and specificity for one centimeter polyps. The serrated polyps,
pre-cancerous lesions predominating on the right, are more difficult to detect.
Keywords: colorectal cancers; screening; average
risk; virtual colonoscopy.
Corresponding author: Boumediene Elhabachi
Received: 23 February,
2019, Accepted: 29 Mars, 2019, English editing:29 Mars, 2019, Published: 1
Avril, 2019.
Screened by iThenticate..©2017-2019 KNOWLEDGE KINGDOM PUBLISHING.
1. Introduction
Colorectal cancer (CRC) is one of the most common
cancers worldwide with 1 million new cases a year [1]. From the epidemiological
point of view, the right colon extends to the splenic fissure, as well as to
the left colic angle (without including it) and the left colon extends from the left colic angle to
the-sigmoid hinge [2]. Seventy-two percent of these cancers are
colonic, of which two thirds are in the left colon, and 28% are rectal. The
localization of the lesions is of great importance in terms of diagnosis,
surveillance, pathophysiology and obviously therapeutic.
Colorectal cancers are sporadic in 75 to 80% of cases [3]. This is essentially the average risk
group aged 50 to 75 years. Subjects at average risk are exposed differently to
environmental hazards and co-morbidities. Several scores have been proposed to
evaluate the risk in this population including the Kaminski score. A
colonoscopy is proposed to them as for the high risk group. "True"
average risk subjects are screened for a trade-off between benefit and risk of
the available means. The cost of CRC is getting more and more expensive and this
trend is confirmed for years to come [4]. This cancer threatens the man in his life
and society in its economy, hence the interest of the issue.
2. Epidemiology
With more than one million cases diagnosed and 500,000
deaths [1] per year worldwide, this cancer is a
public health problem [5]. Colorectal cancer (CRC) is the fourth leading cause
of death in men and the third one in women worldwide. Its incidence increases
with age [6]. The average age at diagnosis in men
(60-65 years) is slightly earlier than in women (65-70 years). In men, the peak
of mortality is between 65 and 70 years old and in the women between 70 and 75
years old. CRC are more common in.
industrialized countries than in developing ones [5].
The CRC is the third most common cancer in the US and
the third leading cause of cancer death [8, 9], while its incidence has declined
significantly over the last four decades [8]. This decrease in incidence is due to
screening programs but also to the trend towards healthier lifestyles [10]. In
2018, newly diagnosed cases were estimated to be at 140,250, say 8.1% of all
new cancer cases, and a death rate of 50,630, or 8.3% of all cancer deaths [11-13 ]. Between 2004 and 2008, the incidence in
men was 55 per 100,000 with a mortality of 20.7 per 100,000 and 41 per 100,000
among women with a mortality of 14.5 per 100,000, while emphasizing that the
incidence was higher for African-Americans [9] .The 5-year survival during the
period 2001-2007 averaged 65.5% for men (55% for African-Americans) and 64.5%
for women (56.9% for Afro-Americans) [14].
3. The Justification for screening
Screening involves detecting colorectal cancer at an
early stage at which the cancer is potentially curable.
Prevention aims to diagnose and remove precancerous
lesions to reduce the incidence of colorectal cancer.
The term "screening" is often used to define
the actual screening but also, by excess of language, prevention.
For justifying screening:
A sufficiently sensitive, specific and non-invasive
screening tool is needed.
It must concern a sufficiently frequent and serious
pathology.
It is necessary to have an effective therapeutic means
of the detected lesions.
The CRCs meet all these criteria [15]. They are
frequent and their screening has made it possible to reduce morbidity and
mortality by CRC. Early cancers have a good prognosis with 89.9% survival at 5
years for stage I, whereas this rate drops to 71.1% in the case of lymph node
involvement [11].
Unfortunately 21% of patients with CRC present a metastasis at diagnosis and about 50% will eventually metastasize, that is what explains the high rate of mortality in these conditions [11,16] and justifies prevention, mass screening and the organization of public awareness campaigns for greater adherence to screening programs [17].
4. Precancerous lesions
It is a benign epithelial tumor, prevalent in the
general population [18] and more common in men than in women.
According to the data of the autopsies, one- third of the population presents
an adenomatous polyp [2, 19]. The term polyp is unsuitable for an adenoma
because a polyp may not be adenomatous. An only pathological examination can
determine the type of polypoid lesion.
Up to 80% of colorectal cancers result from the
malignant transformation of an adenomatous polyp with a first step in the
genesis of the adenoma followed by its growth and then its malignant
degeneration [20].
Among 1000 adenomas, only 100 will reach the size of 1
cm and 37 will increase in size [2]; an invasive carcinoma is found in 9.3%
after a follow-up of 108 months and the cumulative risk of malignancy is 2.5%
at 5 years, 8% at 10 years and 24% to 20 years [21].
The size is a major risk factor for malignant
transformation. This risk is 0.3% for an adenoma less than 1 cm, 9% for an
adenoma of size between 1 and 2 cm and 28% for adenomas greater than 2 cm [2].
In addition to size, which is an important element of
transformation, we must consider the histological types (presence of villous
component) and the presence of severe dysplasia [18, 22].
It is estimated that ten years is the time required
for an adenomatous polyp to degenerate, that is why 10 years are the time
interval for screening after a first normal colonoscopy [23].
According to the World Health Organization WHO classification [27,29] it
is a heterogeneous group consisting of three different entities with different
malignant evolution potential:
- Hyperplastic polyps
They are very common, representing 75% of serrated
polyps. These polyps have no potential for degeneration.
- Sessile
Serrated Adenoma
It represents 15 to 20% of serrated polyps with 90% in the right colon. It occurs in 09% of people who have been colonoscopically examined and are more frequent in women. The risk of transformation is lower than that of a conventional adenoma but the transformation is faster in the case of occurrence of dysplasia or a size greater than 1 cm. In this case the existence of a synchronous degeneration is important and explains why the interval of surveillance between 2 endoscopies is different for the two types of polyps, namely classic or adenomatous and serrated.
- The traditional serrated adenoma
It is rare, with a potential for
degeneration.
Environmental risk factors and
co-morbidities
These are the lifestyle factors. They are modifiable
and increase the risk of cancer, mainly for the average risk group.
-Alcohol consumption
It increases the risk of colorectal cancer
without any difference between the colonic or rectal locations and this risk
increases according to the quantity ingested and the duration of consumption,
the risk increases by 15% for a consumption increase of 100 gr per week [30].
- Smoking
It is a risk factor for adenomas and
colorectal cancers. Compared with non-smokers, smokers and former smokers have
a significantly higher risk of colorectal cancer and death, although the risk
for rectal cancer is greater and evident [31,32].
- Obesity and overweight
The increase in Body Mass Index is associated with an increased risk of colon
cancer in both sexes, but this increase is more pronounced for men, whereas BMI
is a risk factor for the development of rectal cancer, but only in men, which
means that obesity is a risk factor for CRC that depends on sex and the site [33].
- The consumption of meat and
sausages
Red meats [34] (beef, mutton, pork, lamb, goat, and veal)
and deli meats (meat preserved by smoking, drying, salting or adding
preservatives) are criminalized. The risk is increased by 29% for a 100 gr
portion of red meat per day and 21% for a 50 gr portion of deli meats per day [35-37].
5. Average risk group
Everyone is at average risk from the age of 50[38-40].
Age increases, by itself, the risk of colorectal cancer [41]. The risk of a population of 50 to 75
years of developing colorectal cancer without any other risk factor is
estimated between 3.5 [2] and 4.5% [6].
- Men and women between 50 and 74 years
old.
- Asymptomatic people at risk Medium:
• No family history of CCR.
• No personal history of adenoma, serrated polyp or CCR.
• No personal history of chronic inflammatory diseases of intestine.
- Absence of colonoscopy within 5 years.
- No search for occult blood in stools
dating from less than 2 years.
- Absence of serious damage to the general
condition by another cancer for example making this test useless.
- Negative complete colonoscopy within 5 years
or Hemoccult test in the previous 12 months.
- Symptomatology requiring exploration by
colonoscopy: rectorrhagia, melaena,
recent unexplained abdominal pain especially after 50 years old and transitory
disorders of recent occurrence in the form of unusual diarrhea or constipation.
- Increased and very high- risk levels
requiring specific monitoring.
1) Screening by stool tests
"Stool-Based Tests"
They consist of looking for occult blood in
the stool by guaiac test (gFOBT of Fecal Occult Blood
Test), or by immunological test (Fecal immunochemical tests (FITs or iFOBT) and in the search for alterations of the abnormal
exfoliated DNA (search for the APC gene mutation). These tests are not invasive
and require no preparation.
2) Endoscopy: This can be a total
colonoscopy or rectosigmoidoscopy.
3) Virtual colonoscopy.
In the US where colonoscopy is the primary means of screening
[38,42]. Four strategies are possible with the same survival gain and an equal
benefit ratio risk
[39,40]:
- Colonoscopy every 10 years.
- stool test: annual fecal occult blood
test by guaiac test or immune-histochemical test (FIT) or by FIT coupled with
the abnormal DNA test every three years.
- Sigmoidoscopy every 5 to 10 years with
possibly the annual test (FIT).
- Virtual colonoscopy (CTC) every 5 years.
Some countries like France perform mass screening in
two stages. The first is that of selection by the search for occult blood in
the stool (currently the immunological test). In case of positive test and in a
second time called "diagnosis" a colonoscopy is performed.
This approach is based on the argument that a
first-intention colonoscopy will have a very high rate of negative
colonoscopies, so that this examination no longer meets the criteria required
for screening.
6. Evolution of ideas
However, this (French) vision could not ignore the
fact that colonoscopy reduced, although more for the distal than proximal
colon, mortality and the incidence of colorectal cancers [43-44]. Thus, a colonoscopy of Prevention could
be carried out on an individual basis in an average-risk subject after
informing him about the advantages and disadvantages of the examination and
obtaining his informed consent [45].
In addition, the so-called average risk population is
very heterogeneous because people in this group are exposed in a different way
to environmental factors and co-morbidities. Some of them are close to the
high-risk group; they are identified by means of scores [46] and assigned to colonoscopy screening from
the outset [45]. This evolution of ideas in France is
close, at least for one category of subjects, to the American attitude that
proposes, from the start, endoscopy as a means of screening and prevention.
7. Discussion
The incidence, morbidity and mortality of CRCs justify
their prevention and mass screening. For this purpose, colonoscopy is the gold
standard. If colonoscopy was performed as a first-line treatment for the entire
population over the age of 50, the high rate of negative examinations would no
longer allow endoscopy to meet the required criteria for screening. The
severity of this disease, the performance of colonoscopy on the left colon and
the higher frequency of CRCs on the left (2/3 of colon cancers) allowed the
emergence of rectosigmoidoscopy as a good
alternative. Indeed, adenomatous polyps are the most common precancerous lesion
on the left and the detection rate depends on the expertise of the endoscopist. In the right colon serrated polyps are the
most common precancerous lesion. These serrated polyps including sessile
serrated adenomas are difficult to locate and an endoscopist
with a high rate detection of adenomatous polyps does not necessarily have the
same expertise for serrated polyps. Virtual colonoscopy also faces a difficulty
of detection of these polyps. In the USA screening strategies have multiplied
to overcome the invasive nature of colonoscopy. All strategies take into
account epidemiological and pathological data.
In France, as in other countries, stool testing is not
enough for some people who theoretically belong to the average risk group.
Environmental factors and / or co-morbidities rank them in the high-risk group.
These people, outclassed, will benefit from individual screening. Regardless of
these environmental factors and co-morbidities, it is possible to propose a
colonoscopy in an average-risk person after obtaining informed consent.
8. Conclusion
The effectiveness of CRC screening in the average-risk
group is clear. Screening with fecal occult blood testing has proven
effectiveness; this one is, however, inferior to that of endoscopy. This risk
group is no longer considered a homogeneous group and among this group, some
subjects are considered high risk and they are entrusted with endoscopic
screening. In middle-risk people, we can say "true average-risk
group" screening must find a tradeoff between benefit and risk. The VC can
be used as a non-invasive means. It is sensitive and specific for polyps greater
than 1 cm that have a risk of degeneration. In case of particularly multiple
lesions and size larger than 1 cm, a colonoscopy must be performed and the
right colon is de facto explored. Regarding right colon lesions where serrated
polyps are more common, the VC is not very sensitive. This difficulty of
detection being also posed to the colonoscopy, it would perhaps be justified to
propose a search for abnormal DNA or a Fecal immunochemical tests (FITs) in the
saddle in case of negative VC in order to limit the number of lesions missed on
the right and thus to decrease the interval cancers.
9. Conflict of interest statement
We certify that there
is no conflict of interest with any financial organization in the subject
matter or materials discussed in this manuscript.
10. Authors’ biography
No Biography
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