Very rare diseases

According to the European Parliament and Council Regulation (EC) No 141/2000, rare diseases are defined as life-threatening or chronic debilitating conditions with prevalence not surpassing 1 per 2000 European Union citizens. However, the group of rare diseases is considerably heterogeneous comprising some commonly known disorders (e.g. acute leukemia or tuberculosis) as well as entities with prevalence rates not exceeding several cases per one million inhabitants (e.g. certain types of hemophilia) or those where the frequency of occurrence is expressed only as a number of cases described so far (e.g. Schnitzler syndrome or Erdheim-Chester disease).

The National Institute for Health Research, a United Kingdom government body, provides a definition of a group of very rare diseases based on their prevalence not surpassing 1 per 100,000 citizens. In hematology and oncology, several dozen diseases meet this criterion. The Orphanet internet portal ( contains regularly updated data on rare and very rare diagnoses including hematologic and oncologic diseases. Our recently published analysis of the Orphanet database showed that out of 2031 disorders, very rare entities account for the major portion thereof with 1573 entries (77 %). However, oncologic diseases constitute only a small part with 27 very rare tumors and 48 conditions associated with an increased predisposition to malignant transformation. At the same time, it should be stressed here that the Orphanet database is ever expanding. Thus, we suppose that the real figures relating to the group of very rare oncologic disorders are higher.

This internet information portal is focused on very rare diseases reported in patients followed-up at our department. Therefore, the given diagnoses are those where we have direct and long-standing experience in diagnostics and treatment, which reflects in extensive publication activity of our research group. Patients followed-up at our department have also been invited to participate in a registry of very rare hematooncologic diagnoses.

Diagnostic groups of interest:

  • Histiocytoses
  • Systemic mastocytosis
  • Castleman disease
  • Skin manifestations of monoclonal gammopathies
  • Vasculopathies


Szturz P. Very rare diseases in oncology. Med Oncol. 2014; 31: 947.