Cushing’s disease and aggressive pituitary tumours: Aspects on epidemiology, treatment, and long-term follow-up

This thesis focuses on clinical and epidemiological aspects of aggressive pituitary tumours/carcinomas and Cushing’s disease. Pituitary carcinomas account for only 0.1-0.2% of the tumours originating from the anterior pituitary gland and are defined solely by the event of distant metastases, whereas aggressive pituitary tumours are defined by their clinical behaviour of rapid/progressive growth despite optimal treatment with surgery, radiotherapy and medical agents. The prognosis for individuals with aggressive tumours/carcinomas has been poor with few treatment options. However, case reports indicated better outcomes after treatment with the alkylating agent temozolomide. In study I and III , we investigated 24 patients (16 aggressive tumours and 8 carcinomas) given treatment with temozolomide. We found an initial response rate (tumour regression ≥30%) in 10/21 evaluable patients, with complete regression in two carcinomas. Favourable response was associated with low tumour expression of the DNA repair protein MGMT; in responders median 9% (range 5-20%) vs non-responders median 93% (50-100%). Our results also indicated a longer survival in patients with low MGMT. Out of 11 patients with MGMT >10%, nine died with an estimated median survival of 26 months (95% CI 14-38), whereas only 1/6 patients with lower MGMT died from tumour progression during a follow-up of median 83 months (range 12-161). One of the patients in study I and III had a corticotroph pituitary carcinoma and in addition, Lynch syndrome (LS), a hereditary cancer-predisposing syndrome caused by germline mutations in DNA mismatch repair (MMR) genes and primarily associated with colon and endometrial carcinomas. In study II , we investigated the characteristics of the pituitary carcinoma and found loss of MSH2 and MSH6 protein expression, consistent with the patient’s germline mutation in MSH2. This was the first published case of a pituitary tumour associated with LS. In addition, we identified all known Swedish patients with LS (n=910) and searched for diagnostic codes consistent with a pituitary tumour in the Swedish national patient register. We found in total three patients with clinically relevant pituitary tumours, the reported prevalence in the background population is around 1:1000. The last two studies in the thesis focused on Cushing’s disease (CD), i.e. an ACTH-secreting pituitary tumour resulting in excess levels of cortisol. CD is associated with multiple comorbidities and incr