Published data showed that KRAS wild-type metastatic CRC patients who experienced a relative decrease of tumor size >9.66% after 6 weeks of cetuximab-based treatment had a significantly longer median OS compared with all other patients (74.9 weeks versus 30.6 weeks, p = 0.0000025); therefore, ETS might be defined as the decrease in tumor size of at least 10% at the very first radiological assessment since the beginning of treatment [62]. Here, KRAS is linked to colorectal carcinoma.