T test by case/control: p < 0.0001.

## 
##  Welch Two Sample t-test
## 
## data:  marker by group
## t = 4.8821, df = 30.027, p-value = 3.243e-05
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  194.8824 475.1662
## sample estimates:
##    mean in group case mean in group control 
##              491.6341              156.6097

ROC Curve: C-index = 0.828

## 
## Call:
## roc.formula(formula = group ~ marker, data = dat, levels = c("control",     "case"))
## 
## Data: marker in 76 controls (group control) < 28 cases (group case).
## Area under the curve: 0.828
##   threshold specificity sensitivity 
## 151.7573200   0.6578947   0.8571429
##             group
## marker > 152 case control
##        FALSE    4      50
##        TRUE    24      26

Best cutoff 152, where sensitivity = 0.86 and specificity = 0.66.