FIELD : medicine.SUBSTANCE : proposed group of inventions relates to medicine. Disclosed are methods of detecting the presence in a biological fluid sample of a DNA base associated with an extracellular nucleosome, method for assessing an animal subject or individual with respect to suitability for therapeutic treatment, method of observing treatment of an animal subject or human and use of a DNA base associated with an extracellular nucleosome as a biomarker in a biological fluid sample for diagnosing cancer, wherein the DNA base is selected from 5-methylcytosine or 5-hydroxymethylcytosine.EFFECT : proposed group of inventions provides higher clinical sensitivity of cancer diagnosis in animal subject or person.17 cl, 21 dwg, 7 ex