Update: Prolactinoma Radiosurgery

Stereotactic radiosurgery also serves as an option for those refractory to medical and surgical therapy ¹⁾.
GKRS plays a significant role in the treatment of non-functioning [NFA] and hormonal-active [HAA] pituitary adenoma. It affords high rate of tumor control and offers low risk of collateral neurological or endocrine axis injury. A study showed that control of tumor growth was achieved in 90% patients, shrinkage of tumor in 54% and arrest of progression in 36% cases after GKRS treatment. The biochemical remission rate in GH secreting adenoma was 57%, ACTH adenoma was 67% and prolactinoma was 40%. Age less than 50 years and tumor volume less than 5cm3 were associated with a favourable radiosurgical outcome ²⁾.

Radiotherapy as an alternative and adjuvant treatment for prolactinomas has been performed at the Department of Radiation Oncology, Prince of Wales Cancer Centre, Sydney, New South Wales, Australia, with the linear accelerator since 1990.
In a retrospective review of 13 patients managed with stereotactic radiosurgery (SRS) and 5 managed with fractionated stereotactic radiotherapy (FSRT), as well as 5 managed with conventional radiotherapy, at the Prince of Wales Hospital. Patients with a histopathologically diagnosed prolactinoma were eligible. Those patients who had a confirmed pathological diagnosis of prolactinoma following surgical intervention, a prolactin level elevated above 500 μg/L, or a prolactin level persistently elevated above 200 μg/L with exclusion of other causes were represented in this review.
At the end of documented follow-up (SRS median 6 years, FSRT median 2 years), no SRS patients showed an increase in tumour volume. After FSRT, 1 patient showed an increase in size, 2 showed a decrease in size and 2 patients showed no change. Prolactin levels trended towards improvement after SRS and FSRT, but no patients achieved the remission level of <20 μg/L. Seven of 13 patients in the SRS group achieved a level of <500 μg/L, whereas no patients reached this target after FSRT.
A reduction in prolactin level is frequent after SRS and FSRT for prolactinomas; however, true biochemical remission is uncommon. Tumour volume control in this series was excellent, but this may be related to the natural history of the disease. Morbidity and mortality after stereotactic radiation were very low in this series ³⁾.

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Cohen-Inbar et al., reviewed the outcome of patients with medically and surgically refractory prolactinomas treated with Gamma Knife radiosurgery (GKRS) during a 22 years follow-up period.
They reviewed the patient database at the University of Virginia Gamma Knife center during a 25-year period (1989-2014), identifying 38 patients having neurosurgical, radiological and endocrine follow-up.
Median age at GKRS treatment was 43 years. Median follow-up was 42.3 months (range 6-207.9). 55.3 % (n = 21) were taking a dopamine agonist at time of GKRS. 63.2 % (n = 24) had cavernous sinus tumor invasion. Endocrine remission (normal serum prolactin off of a dopamine agonist) was achieved in 50 % (n = 19). GKRS induced hypopituitarism occurred in 30.3 % (n = 10). Cavernous sinus involvement was shown to be a significant negative prognosticator of endocrine remission. Taking a dopamine agonist drug at the time of GKRS showed a tendency to decrease the probability for endocrine remission.
GKRS for refractory prolactinomas can lead to endocrine remission in many patients. Hypopituitarism is the most common side effect of GKRS ⁴⁾.

evaluated the efficacy of Gamma knife stereotactic radiosurgery (GKSR) as an adjunctive management modality for patients with drug resistant or intolerant cavernous sinus invasive prolactinomas. Twenty-two patients with cavernous sinus invasive prolactinoma underwent GKSR between 1994 and 2009. Thirteen patients were dopamine agonist (DA) resistant. Six patients were intolerant to DA. Three patients chose GKSR as their initial treatment modality in hopes they might avoid life long suppression medication. The median tumor volume was 3.0 cm3 (range 0.3–11.6). The marginal tumor dose (median= 15 Gy, range 12–25 Gy) prescribed was based on the dose delivered to the optic apparatus. The median follow-up interval was 36 months (range, 12–185). Endocrine normalization was defined as a normal serum prolactin level off DA (cure) or on DA. Endocrine improvement was defined asa decreased but still elevated serum prolactin level. Endocrine deterioration was defined as an increased serum prolactin level. Endocrine normalization was achieved in six(27.3%) patients. Twelve (54.5%) patients had endocrine improvement. Four patients (18.2%) developed delayed increased prolactin. Imaging-defined local tumor control was achieved in 19 (86.4%) patients, 12 of whom had tumor regression. Three patients had a delayed tumor progression and required additional management. One patient developed a new pituitary axis deficiency after GKSR. Invasive prolactinomas continue to pose management challenges. GKSR is a non invasive adjunctive option that may reduce prolactin levels in patients who are resistant to or intolerant of suppression medication. In a minority of cases, patients may no longer require long term suppression therapy ⁵⁾.

Twenty-three patients were included in analysis of endocrine outcomes (median and average follow-up of 55 and 58 mo, respectively) and 28 patients were included in analysis of imaging outcomes (median and average follow-up of 48 and 52 mo, respectively). Twenty-six percent of patients achieved a normal serum prolactin (remission) with an average time of 24.5 months. Remission was significantly associated with being off of a dopamine agonist at the time of GKRS and a tumor volume less than 3.0 cm3 (P < 0.05 for both). Long-term image-based volumetric control was achieved in 89% of patients. Complications included new pituitary hormone deficiencies in 28% of patients and cranial nerve palsy in two patients (7%).
Clinical remission in 26% of treated patients is a modest result. However, because the GKRS treated tumors were refractory to other therapies and because complication rates were low, GKRS should be part of the armamentarium for treating refractory prolactinomas. Patients with tumors smaller than 3.0 cm3 and who are not receiving dopamine agonist at the time of treatment will likely benefit most ⁶⁾.

Twenty patients with prolactinomas were followed after GKS. Five patients were treated successfully; their prolactin (PRL) levels dropped into the normal range and dopaminergic drugs could be discontinued. Two spontaneous pregnancies were observed and 11 patients experienced improvement. Improvement was defined as normal PRL levels with the continued possibility of reduced medical treatment or a substantially reduced medical treatment dose with some degree of hyperprolactinemia maintained. The treatment failed in three patients who experienced no improvement. Patients treated with dopaminergic drugs during GKS did significantly less well in comparison with the untreated group when a cumulative distribution function (Kaplan-Meier estimate) was used. CONCLUSIONS:
The results of GKS for prolactinomas in this investigation are better than the results published by others. This may be an effect of case selection because there were no “salvage cases” in our group of patients. Because a dopamine agonist seemed to induce radioprotection in this series, it is suggested that GKS be performed during an intermission in drug therapy when the dopamine agonist is discontinued ⁷⁾.