Colorectal cancer is characterised by the unchecked survival and division of abnormal cells resulting in an abnormal growth in the rectum or colon [1]. It is responsible for 400,000 deaths annually and is globally one of the most common tumours [2]. The age standardized rates of CRC have increased to 11 per 100,000 in males and increased to 9.2 per 100,000 in females from 2011 to 2015 in Uganda [3,4]. The major risk factors for CRC in the Ugandan population are smoking, alcohol consumption and urbanization [4].

In 1965 Gold and Freedman observed that the CEA molecular marker is present in fetal gut tissues and in tumours of the gastrointestinal tract [5]. Intercellular adhesion of colon collagen-epithelial cell interactions is modulated by CEA [6]. The development of less ordered tissues due to more cell movement results from high concentrations of CEA which disrupts normal intercellular or cell-collagen adhesion forces between the cancer cells [6]. The greatest clinical use of CEA appears to be in the follow-up for recurrent disease and in the evaluation of treatment efficacy [6].

The most commonly used tumour marker for diagnosis of CRC, tumour recurrence and evaluation of prognosis is CEA [7]. The CEA molecular marker is found in low concentrations in the human plasma and in foetal gastrointestinal tissue. Its concentration increases in colorectal cancer and also in gastric cancer, ovarian cancer, uterine cancer, bronchial tumours and lymphomas [8].

An increased growth of the colorectal tumour is associated with a poorer prognosis and a high CEA production [9,10]. Although the role of CEA in the prognosis of CRC remains controversial, it may be measured quantitatively and detected in the tumour tissues and serum of CRC patients [11].

Current ASCO guidelines recommend 1-3 month interval CEA examinations, for the systemic treatment of metastatic CRC and a 3-monthly interval for CEA examinations during postoperative surveillance [10]. Factors which have been found to affect plasma CEA levels include tumour grade, stage, and location of tumour, ploidy status of the tumour, absence or presence of bowel obstruction and liver status.

The objective of this study was to investigate the relation between plasma CEA among the tumour stage, grade, topography and histopathological subtype of colorectal adenocarcinoma in Ugandan patients.

From 16^th September 2019 to 16^th September 2021, blood samples were obtained from colorectal cancer patients in Masaka Regional Referral Hospital, Mulago National Referral Hospital, Uganda Martyrs’ Hospital Lubaga and Mengo Hospital. There were 119 consecutively recruited participants with corresponding blood samples for CEA analysis. Using a standard pretested Data Extraction Form, data for all the participants was extracted from the clinical patients’ files in the respective hospitals. The data included age, sex, grade, and topography of colorectal cancer.

A 10mls blood sample was obtained from the 119 prospectively recruited participants, preoperatively to obtain the plasma CEA level and these blood samples were transported using a cold chain system at 4-80C to the Department of Immunology and Molecular Biology, School of Biomedical Sciences, College of Health Sciences, Makerere University. The inclusion criteria for the preoperative plasma CEA levels included patients with index histologically diagnosed colorectal adenocarcinoma and patients had to be willing to provide their blood samples for plasma CEA analysis preoperatively. Blood samples with incomplete or unavailable data were excluded. All plasma samples for CEA were stored at 4-80C.

Right-sided colon tumours included colon cancer of the caecum, ascending colon and hepatic flexure as defined by the American Society of Clinical Oncology (ASCO). Left-sided colon tumours comprised of colon cancer in the splenic flexure, descending colon and rectum [12,13].

Statistical Analysis

Continuous numeric data were summarized by mean (standard deviation) and categorical data were summarized as frequencies and percentages. Mean CEA levels were compared by the student’s t-test where the independent variable had two levels (age and sex), and the ANOVA test with the corresponding F-statistic where the independent variable had three or more levels. CEA levels were further categorised into two group: a) ≤mean CEA (ng/ml) and b) above mean CEA (ng/ml); Pearson chi-square tests were conducted to test for associations between categorised CEA levels and selected independent variables. In all statistical tests, a p-value of ≤0.05 was considered statistically significant.

Table 1 shows the demographic characteristics of the patients. The recruited CRC patients consisted of 48 (43.2%) females and 63 (56.7%) males.

The most common tumour location were rectal tumours 51 (50%) followed by 27 (26.5%) left-sided colon tumours and 24 (23.5%) right-sided colon tumours. Histopathological examinations showed 9 (9.2%) well-differentiated tumours, 75 (76.5%) moderately differentiated tumours and 14 (14.3%) poorly differentiated colorectal tumours. Classical adenocarcinoma (AC) was the most common histopathological subtype 94 (87%), followed by MAC 7 (6.5%) and SRCC 7 (6.5%). The majority of colorectal tumours were stage III 34 (31.8%) followed by stage IV, 29 (27.1%) colorectal tumours. Stage I constituted 16 (14.9%) tumours and stage II constituted 28 (26.2%) tumours.

The mean age of all the participants was 55.9 (±15.3) years whilst the mean CEA level was 23.6 (±8.51) ng/ml. The median CEA level was 23.2 (IQR: 16.5-30.7) ng/ml.

Table 1: Demographic and clinicopathological characteristics of the CRC patients.

There were 27 (52.9%) rectal cancers below the mean plasma CEA level whilst there were 24 (47.1%) rectal cancers that were above the mean plasma CEA level. Right-sided colon cancers included 12 (50%) above the mean plasma CEA level. There were 12 (44.4%) left-sided colon cancers with a below the plasma mean CEA level, while there were 15 (55.6%) left-sided colon cancers with a plasma CEA level above the mean. There was no difference in plasma CEA level between rectal, right-sided and left-sided colon cancers. Pearson chi2 (2) = 0.5098; p=0.775.

Stage I colorectal tumours consisted of 10 (62.5%) below the mean plasma CEA levels and 6 (37.5%) above the mean plasma CEA levels. There were 14 (50%) stage II colorectal tumours with a below plasma mean CEA level and 14 (50%) stage II colorectal tumours with an above plasma mean CEA level. Stage III colorectal tumours consisted of 17 (50%) having a below mean plasma CEA level and 17 (50%) having an above plasma CEA level. There were 14 (48.3%) colorectal tumours with a below plasma mean CEA level whilst there were 15 (51.7%) colorectal tumours with an above plasma mean CEA level. There was no difference in plasma CEA levels between stage I, II, III or IV colorectal tumours; Pearson chi (2) (3) = 0.9511; p=0.813.

There were 3 (33.3%) well-differentiated colorectal tumours with a below the mean plasma CEA level whilst there were 6 (66.7%) that had an above the mean plasma CEA level. Moderately-differentiated CRC consisted of 39 (52%) with a below the mean plasma CEA and 36 (48%) with an above the mean plasma CEA. There were 8 (57.1%) poorly-differentiated colorectal tumours with a below the mean plasma CEA level while there were 6 (42.9%) poorly-differentiated CRC’s with an above the mean plasma CEA level. There was no difference between the grade of CRC and the plasma CEA level. Person chi2 (2) =1.37; p=0.505.

Classical adenocarcinoma (AC) consisted of 49(52.1%) colorectal tumours with a below the mean plasma CEA level while 45 (47.9%) colorectal tumours with an above the mean plasma CEA level. There were 4 (57.1%) colorectal tumours with a below the mean plasma CEA level while 3 (42.9%) colorectal tumours had an above the mean plasma CEA level. Signet ring colorectal carcinoma consisted of 4 (57.1%) CRC’s having a below the mean plasma CEA level and 3 (42.9%) CRC’s having an above the mean plasma CEA level. There was no difference in plasma CEA levels between AC, MAC and SRCC colorectal tumours; Pearson chi (2) (3) = 0.1230; p=0.940.

Table 2: Comparison of plasma carcinoembryonic antigen (CEA) levels with different clinicopathological features of colorectal cancer.

Table 2 shows the comparison of plasma carcinoembryonic antigen (CEA) levels with different clinicopathological features of colorectal cancer. There was no difference in CEA level with age, sex, topography, grade, stage, histopathological subtype and LVI status (Table 2).

Globally carcinoembryonic antigen (CEA) is the most widely and frequently used tumour marker in CRC [14]. In this study there was no significant difference in mean CEA among the well- and moderate- and poorly- differentiated CRC. This is in contrast to other studies which found that CEA tends to be higher in patients with well-differentiated colorectal adenocarcinoma [15,16]. Increasing tumour stage in our study was also not associated with an increase in plasma CEA. Many patients presented with poorly differentiated tumours and this may explain why some patients with advanced-stage CRC do not exhibit an increased plasma CEA level [15].

Some reports suggest that compared to right-sided colon cancer, patients with left-sided colon cancer generally have a greater incidence of increased plasma CEA levels [17,18]. However, in our study there was no difference in plasma CEA levels between right-sided colon cancer and left-sided colon cancer.

In a study by Agusrly Chandra, the Kruskal-Wallis test showed that with increasing histopathological grading of colorectal cancer, the plasma CEA levels increase [19] Therefore, it was concluded that there were differences in plasma CEA level based on histopathological grade. These findings were similar to those in a study by Wesley, [20] but in contrast to findings in our study which showed no difference in plasma CEA level based on histopathological grade.

There is an inability of the cells to polarize and express CEA on the colorectal cell surface due to neoplasm cells located in the tumour gland and disruptions in the structure of normal tissue. Therefore, there is an effect on the distribution of CEA in the lymph vessels through the intercellular space and blood vessels. This leads to those patients showing poor differentiation, resulting in increased plasma CEA levels reported in some studies [21]. However, this is in contrast to several previous studies which have shown higher plasma CEA levels in well-differentiated colorectal cancer [22].

Smoking appears to double the plasma CEA concentration and may contribute to the increased CEA levels seen in patients with pancreatitis and alcoholic liver disease. Elevated plasma CEA levels may occur in patients with hepatic disorders and gastrointestinal disorders. These disorders produce less than 10ng/ml of plasma CEA. Approximately 50% of patients with severe benign hepatic disease have an elevated plasma CEA level [23]. These benign diseases include active alcoholic cirrhosis, chronic active and viral hepatitis and biliary and cryptogenic biliary cirrhosis. Patients with cholangitis and liver abscess which are forms of extrahepatic biliary obstruction may have elevated plasma CEA levels. In patients with active ulcerative colitis, the increased circulating CEA levels tend to correlate with the severity and extent of the disease [23]. Therefore, when interpreting an elevated CEA level in the gastrointestinal tract, one must consider malignant as well as benign aetiologies.

Our study concluded that there was no difference in plasma CEA levels based on histopathological grade, stage, location and histopathological subtype of CRC. Therefore, the plasma CEA levels in Ugandan patients did not increase with increasing histopathological grade and stage, and was not affected by the location and histopathological subtype of colorectal tumour.

A limitation for analyzing the preoperative plasma CEA levels in the prospective arm of the study was that different time intervals elapsed between plasma CEA measurement concentrations and colorectal resection. Underrating or overrating the plasma CEA level may have influenced the outcome of the study due to the timing of measurement of plasma CEA.

Ethical Approval

This study was part of the PhD work, which was approved by the Doctoral Committee and Higher Degrees Research and Ethics Committee of the School of Biomedical Sciences, College of Health Sciences, Makerere University for the corresponding author (SBS-HDREC-630). Final approval of this research study was obtained from the Uganda National Council for Science and Technology (HS-2574).

Consent for Publication

Consent was obtained from all the participants enrolled in this study.

Competing Interests

The authors declare that they have no competing interests.

Funding

The authors declare that they received no specific funding for this work. However, the corresponding author personally funded this part of his PhD research study. No payment was received by the authors to write and publish this part of the study.

Authors’ Contributions

Richard Wismayer conceived the concept and proposal, collected data, performed data analysis and wrote the first draft. Julius Kiwanuka performed data analysis and provided statistical support. Michael Odida and Henry Wabinga performed critical reviews of the manuscript for intellectual content. All authors approved the final manuscript for publication.

Acknowledgements

The authors wish to thank the clinical staff and research assistants, particularly Dr. Sulaiman Ishaq Mahmud and Dr. Justus Atuhaire who recruited the participants from the Department of Surgery of Masaka Regional Referral Hospital, Mulago National Referral Hospital, Uganda Martyrs’ Hospital Lubaga and Mengo Hospital for their support in this research project. Lastly, we are also grateful to Mr Francis Wasswa for the laboratory technical work for plasma CEA analysis which was carried out for this part of the research project in the Department of Immunology and Molecular Biology, School of Biomedical Sciences, College of Health Sciences, Makerere University.

Abbreviations

CRC – Colorectal cancer

CEA – Carcinoembryonic antigen

LVI – Lymphovascular invasion

AC – Classical adenocarcinoma

MAC – mucinous adenocarcinoma

SRCC – Signet ring colorectal carcinoma

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