The present study aimed at comparing the photo detection of peritoneal micrometastases in an ovarian cancer model
following administration of two precursors of protoporphyrin IX (PpIX): aminolevulinic acid (ALA) and hexylester
ALA or He-ALA (100mg/kg) was injected in the peritoneum cavity of 16 rats with induced peritoneal metastases of
ovarian cancer. Two hours later, the tumours were visualized laparoscopically using both white light for standard
exploration and blue light for fluorescence (D-light, Karl Storz, Tuttlingen, Germany). Peritoneal micrometastases were
counted. The distribution of PpIX through the peritoneum was studied on frozen biopsies using fluorescence microscopy
and correlated with pathological findings.
The number of micrometastases detected by the fluorescence blue mode was significantly higher (p<0.05) than with
standard white light for both ALA (235 versus 198) and He-ALA application (248 versus 199). The mean fluorescence
intensity ratio between tumor and normal surrounding tissue was significantly (p< 0.05) higher for He-ALA (1.6±0.1)
compared to ALA (1.4±0.1). Fluorescence microscopy confirmed that the fluorescence remained limited to cancer cells.
Macroscopically fluorescing nodules were histopathology confirmed as malignant.
In conclusion, He-ALA is an excellent precursor for PpIX synthesis giving the highest PpIX fluorescence contrast
between normal and tumoral peritoneum. Imaging with He-ALA improves the detection of peritoneal metastases
comparing to ALA.