MATERIAL AND METHODS
Study design
A retrospective observational cohort study was conducted.
Study population
We studied 194 patients diagnosed with colorectal cancer (stages I-IV).
All patients were over 18 years old and had been treated by the Oncology
Unit of the Virgen de las Nieves University Hospital (HUVN) between 2000
and 2016. Patients with other types of colorectal cancer, synchronous
neoplasms and those whose Clinical histories were incomplete were
excluded. The study was approved by the HUVN Ethics and Research
Committee, and was conducted according to the Declaration of Helsinki.
Clinical and sociodemographic
variables
Clinical and sociodemographic data were collected from clinical
histories: sex, diagnosis, date and age of diagnosis, surgery, tumor
size, stage, ECOG (Eastern Cooperative Oncology Group) Performance
Status, histopathological type, date of death and scheme of chemotherapy
treatment. Tumor stage was determined according to the TNM
classification of the AJCC (American Joint Committee of
Cancer)(15).
Genetic variables
DNA was extracted from paraffin tumor samples from the Biobank of
Andalusia (Collection Code: 19150007). The QIAamp DNA Mini Kit was used
following the manufacturer’s instructions and stored at -40 ° C.
Gene mutations were analyzed by Real-Time PCR using TaqMan® probes:KRAS codons 12, 13 and 61 (rs121913529, rs121913530, rs121913535,
rs112445441, rs17851045, rs121913238, rs121913240), NRAS codons
12, 13 and 61 (rs121913237, rs121434596, rs11554290, rs121913254),BRAF (rs113488022), PIK3CA exons 9 and 20 (rs121913273,
rs104886003, rs121913281, rs121913279). Positive samples were confirmed
by Sanger DNA Sequencing.
Outcome variables
Overall survival was the primary endpoint, and was defined as time from
the diagnosis of CRC until death from any cause. The end date of the
study was used when the death event had not occurred.
Statistical analysis
The normal distribution of the variables was determined using the
Shapiro-Wilks test. Quantitative non-normally distributed variables were
described by median and percentiles (25 and 75). Qualitative variables
were expressed as frequencies.
The Kaplan-Meier method and the log-rank test were used to evaluate the
influence of clinical, genetic and sociodemographic variables on
survival (bivariate analysis). Multivariate Cox proportional hazard
regression model was used to obtain the adjusted hazards ratio (HR) and
95% confidence interval (CI95%) for potential prognostic factors for
survival.
The significance level for all the tests was p <0.05. The
software used for the survival analysis was EZR 1.35 (R
2.3.0)(16).