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There are no prognostic variables indicating how many lines of therapy patients will receive and whether later lines could be effective. Among 420 subjects, joint probabilities for a patient submitted to first-line therapy to receive further lines were: second line, 74.3%; third line, 47.0%; and fourth line, 21.6%. Moreover, 31% of the patients with early progression during first-line therapy experienced a clinical benefit with later lines.The optimal therapeutic strategy for metastatic colorectal cancer patients is still a matter of debate. There are no prognostic variables indicating how many lines individual patients ought to receive, and whether later lines could be effective even when earlier ones were not.We retrospectively collected data from 420 consecutive patients with metastatic colorectal cancer at our institution, describing the proportion of patients who received second or later lines of therapy and the chance of a line of treatment being active when the previous line was not. For each line of treatment, we defined clinical benefit as the probability of not having had evidence of disease progression 6 months after the start of chemotherapy.Of the 373 patients with disease progression after first-line chemotherapy (1L), 277 received a second line (2L) (probability of being submitted to a 2L (P(2L)) = 74.3%): 143 (63.3%) of 226 received a 3L (P(3L)), and 56 (45.9%) of 122 were submitted to a 4L (P(4L)). Joint probabilities were: 2L 74.3%, 3L 47.0%, and 4L 21.6%. A total of 298 (71.5%) of 417 patients had a clinical benefit with 1L; 134 (48.6%) of 276 with 2L; 50 (35.2%) of 142 with 3L; and 12 (25.0%) of 48 with 4L. Taking all these data together, 31% of the patients who experienced early progression at 1L had the chance to have a clinical benefit with any further lines.Our study demonstrated that of 4 patients submitted to a 1L, about 3 will receive a 2L, about 2 a 3L, and nearly 1 a 4L. Later lines could be beneficial even though earlier ones were not.