This disclosure provides methods of identifying or selecting a patient most likely to benefit from treatment with a telomerase inhibitor, such as e.g. imetelstat, by testing a patient for: a lack of a mutation in each of JAK2, CALR, and MPL; and/or a high-molecular risk (HMR), based on the presence of a mutation in at least one of the following genes: ASXL1, EZH2, SRSF2, and IDH1/2. The patient may be suffering from myelofibrosis. The disclosure also provides methods of treating myelofibrosis, which include identifying such patients.