You added the
as.factor(dataCancer$Classification) in the script, but even if the dataset dataCancer is attached, a command like the one above does not transform the dataset variable Classification into a factor. It only returns a factor on the console.
Since you want to fit the model on the training dataset, you either specify
training_data$Classification <- as.factor(training_data$Classification) classification_model <- glm(Classification ~ ., data = training_data, family = binomial)
or use the as.factor function in the glm line code
classification_model <- glm(as.factor(Classification) ~ ., data = training_data, family = binomial)