Table 1.

Clinical characteristics of patients and histology of CRMs by Bosniak stratification.

	Bosniak IIF	Bosniak III	Bosniak IV	P value
Patients, n/N (% of total)	287/532 (53.8)	139/532 (26.1)	106/532 (19.9)
Age at diagnosis, mean, years ± SD	63 ± 13.3	64 ± 13.6	63 ± 14.0	0.597
Sex, n (% of Bosniak class)				0.666
Male	182/287 (63.4)	82/139 (58.9)	62/106 (58.5)
Female	107/287 (36.6)	57/139 (41.0)	44/106 (41.5)
Size of cystic mass, median, cm (IQR)	2.60 (1.5–4.8)	2.90 (2.0–5.1)	4.3 (2.8–6.1)	< 0.001*
Renal mass biopsy, n (% of Bosniak class)	9 (3.1)	18 (12.9)	7 (6.6)	< 0.001
Follow-up time, median (IQR), months	64 (51–88)	62 (48–104)	73 (47–105)	0.442**
Initial surgery, IS, n/N (% of Bosniak class)	1/287 (0.3)	54/139 (38.8)	85/106 (80.2)
Active surveillance, AS	286/287 (99.7)	85/139 (61.2)	21/106 (19.8)	< 0.001
Surveillance only	276/287 (96.1)	67/139 (48.2)	6/106 (5.7)
Delayed surgery, DS	11/287 (3.8)	18/139 (12.9)	15/106 (14.2)
Surgical treatment, IS + DS	12/287 (4.2)	72/139 (51.1)	100/106 (94.3)	< 0.001
Radical nephrectomy	1/287	18/139	45/106
Partial nephrectomy	11/287	54/139	55/106
Malignant histology of operated CRMs, n/N (% of Bosniak class)	5/12 (41.7)	56/72 (77.8)	88/100 (88.0)	0.014 (IIF vs III), 0.001 (IIF vs IV), 0.062 (III vs IV)
Histological subtypes, n (% of malignant histology)				0.261
ccRCC	3 (60)	35 (62.5)	63 (71.6)
Papillary RCC	2 (40)	11 (19.6)	21 (23.9)
Type I	2	5	7
Type II	0	2	6
Unspecified	0	4	8
Multilocular cystic RCC	0	6 (10.7)	2 (2.3)
Chromofobe RCC	0	3 (5.3)	2
Translocation carcinoma	0	1 (1.7)	0

CRM complex cystic renal mass, ccRCC clear cell renal cell carcinoma, RCC renal cell carcinoma.

P values were calculated using the Kruskall–Wallis and Fisher exact test.

*IIF versus III p = 0.447, IIF versus IV p < 0.001, III versus IV p < 0.001.

**IIF versus III p = 0.684, IIF versus IV p = 0.107, III versus IV p = 0.428.