Table 1.

A brief description of studies and their main findings used in the present review

Study	Diagnosis	Number of patients	Control	Capacity assessment	Test timepoint (consent)	Main findings
Triebel et al. [18]	Malignant glioma	26	Yes	CCTI	Average time from diagnosis = 6.9 months	Over 50% of patients showed compromised capacity in medical decision-making. Cognitive performance on verbal acquisition and recall, in addition to semantic fluency, predicted performance of the appreciation, reasoning, and understanding standards of consent.
Marson et al. [30]	Malignant glioma	26	Yes	CCRI	Average time from diagnosis = 6.9 months	Malignant glioma patients performed significantly below the controls on the consent standards of appreciation, reasoning, and understanding. Around one-third of patients showed compromised capacity. Phonemic and semantic verbal fluency found to predict CCRI performance.
Kerrigan et al. [29]	Radiologically suspected intracranial tumour	100	No	MacCAT-T	Preoperative (no consent required)	25% of patients lacked mental capacity to give valid consent to neurosurgery, of which almost half were missed on initial capacity assessment by the neurosurgical team. Patients lacking mental capacity were significantly more cognitively impaired than those with capacity. ACE-R semantic verbal fluency performance and ability to repeat 7-item name and address after three attempts were predictive of incapacity.
Gerstenecker et al. [31••]	Brain metastasis	41	Yes	CCTI	Within a week before starting RT	The understanding facet of capacity was associated with a range of cognitive performances. Also, performance in phonemic fluency and verbal memory were found to be predictors of capacity to understand a treatment decision.
Gerstenecker et al. [32••]	Brain metastasis	41	Yes	CCTI	Within a week before starting RT	The reasoning facet of capacity shared significant associations with two cognitive performance aspects. Also, episodic memory and processing speed performance were found to be predictive of capacity to reason through a treatment decision.

*Patients with a diagnosis of either a primary or metastatic brain tumour were included in the study

Requirements—direct assessment of capacity using either MACCAT-T or CCTR/CCRI

ACE-R, Addenbrooke’s Cognitive Examination-revised; CCRI, Capacity to Consent to Research Instrument; CCTI, Capacity to Consent to Treatment Instrument; KPS, Karnofsky Performance Scale; MACCAT-T, MacArthur Competence Assessment Tool for Treatment