Rare cancers

The definition of rare tumors is not consensual. Rare cancers are defined as an incidence of fewer than 6 cases per 100.000 individuals per year (RARECARE workin group, Gatta et al. Eur J Cancer 2011).

According to DeSantis et al. ACS Atlanta. CA Cancer J Clin 2017, overall, approximately 20% of patients with cancer in the United States are diagnosed with a rare cancer. Based on the RARECARE workin group, Gatta et al. Eur J Cancer 2011, rare cancers are about 22% of all cancer diagnoses in Europe and 24% of the total cancer prevalence.

Rare cancers include > 300 histological subtypes and may affect all organs (Morfouace et al. EORTC, ESMO Open 2020). In addition, they can be grouped within 12 families of rare cancers (Casali et al. Fondazione IRCCS INT, Milan, ESMO Open 2020):

1. Epithelial tumours of head and neck:
• Larynx;
• Hypopharynx;
• Nasal cavity and sinuses;
• Nasopharynx;
• Major salivary glands and salivary gland type tumours;
• Oropharynx;
• Oral cavity and lip;
• Eye and adnexa;
• Middle ear.
2. Epithelial digestive tumours:
• Small intestine;
• Anal canal;
• Gallbladder and extrahepatic biliary duct.
3. Thoracic tumours:
• Epithelial tumours of the trachea;
• Thymomas and thymic carcinomas;
• Malignant mesothelioma.
4. Female genital tumours:
• Non-epithelial tumours of the ovary;
• Epithelial tumours of the vulva and vagina;
• Trophoblastic tumours of the placenta.
5. Male genital and urogenital tumours:
• Tumours of the testis and paratestis;
• Epithelial tumours of penis;
• Extragonadal germ cell tumours;
• Epithelial tumours of renal pelvis, ureter, and urethra.
6. Skin cancers and non-cutaneous melanoma:
• Mucosal melanoma;
• Uveal melanoma;
• Adnexal skin carcinomas;
• Kaposi sarcoma.
7. Sarcomas:
• Soft tissue sarcoma;
• Bone sarcoma;
• Gastrointestinal stromal tumours.
8. Neuroendocrine tumours:
• Gastrointestinal pancreatic;
• Lung;
• Other sites.
9. Endocrine organ tumours:
• Thyroid cancers;
• Parathyroid cancer;
• Adrenal cortex cancer;
• Pituitary gland cancer.
10. Central nervous system tumours:
• Glial tumours and others;
• Malignant meninioma;
• Embryonal tumours.
11. Paediatric tumours:
• Hepatoblastoma;
• Neuroblastoma and ganglioneuroblastoma;
• Nephroblastoma;
• Odontogenic malignant tumours;
• Olfactory neuroblastoma;
• Pancreatoblastoma;
• Pleuropulmonary blastoma;
• Retinoblastoma.
12. Haematological malignancies:
• Lymphoid malinancies;
• Myelodysplasctic syndromes;
• Myeloproliferative neoplasms (including mastocytosis);
• Myelodysplastic/myeloproliferative neoplasms;
• Myeloid/lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA (platelet derived growth factor receptor alpha), PDGFRB (platelet derived growth factor receptor beta), or FGFR1 (fibroblast growth factor receptor 1), or with PCM1-JAK2 (pericentriolar material 1-janus kinase 2);
• Acute myeloid leukaemia and related neoplasms.

Then, rare cancers are not so rare, and they are associated with multiple challenges including late and incorrect diagnosis, adverse outcomes, limited clinical expertise, weak evidence for best practice, and difficulties in collecting large series for research and in carrying out clinical trials (Boyd et al. BCCA, Vancouver, Lancet Oncol 2016).

Therefore, a global strategy is needed to join efforts to increase knowledge of this group of cancers.