Introduction
Bladder tumour volume is difficult to calculate. Using a new technique we have seen that there are significant differences between the histological subtypes compared to transitional cell cancer. This estimation of tumour volume affects prognosis.
Methods
We retrospectively measured the parameters of length and width of tumour post radical cystectomy. We had a total of 236 cases. We estimated tumour volume by assuming the 3^{rd} dimension to be 50% of the width. We then used the ellipsoid tumour calculator LxHxWxpi/6 to give an approximation to the volume.
Pathologists do not ordinarily estimate tumour volume on cystectomy specimens. They will record the two largest diameters, the length and width. The tumours are irregular in shape and can be multifocal. We made two assumptions estimating the volume. The third parameter has to be less than the second, by definition, and we chose 50%. We used the ellipsoid calculation that has been used for prostate gland estimation successfully.
We also included the volume of TURBT chippings from the TURBT immediately prior to the cystectomy and summated the two.
We then peformed regression analysis to determine the significant predictors of mortality.
Results

Squamous cell cancer

Neuroendocrine cancer

Sarcomatous cancer

adenocarcinoma

Metastatic cancer

Transitional cell cancer

N patients

15

7

9

3

4

198

Mean cc

106

33

36

3

11

15

Standard deviation

152

62

45

4

10

29

T test compared to TCC

7

1.4

2

0.7

0.3


P compared to TCC

<0.0001

0.14

0.046

0.46

0.76


Cox proportional hazards regression
Covariate b SE Wald P
Age 0.02070 0.009677 4.5742 0.0325
CIS2 0.3911 0.1903 4.2267 0.0398
PSM 0.7736 0.2484 9.7000 0.0018
T_Stage=3 0.7904 0.2113 13.9912 0.0002
T_Stage=4 1.1074 0.2529 19.1662 <0.0001
volume_cc 0.005819 0.001380 17.7719 <0.0001
Discussion
The mean tumour volume of the most common subtype, transitional cell cancer, is 15cc. There was no significant difference between neuroendocrine, sarcomatous, adeno and metastatic subtypes. There was a significant difference in the size of sarcomatous variants with a mean volume of 36cc and the enormous size of squamous tumours with a mean volume of 106cc. We note that half of the squamous tumours were of low or medium grade which may have a bearing on how they can reach this size. Regression analysis shows the known predictors of mortality plus, significantly, the amount of tumour volume using this model.
We realise this is a rough approximation to the true tumour volume. However, it is a systematic error and will still yield differences in histological subtypes. Tumour volume should be included as a prognostic risk factor to advise decisions making post TURBT and further managment post cystectomy.