The anti-cancer effects of the phytochemicals present in the crude extract may vary from cells to cells. All cytotoxic drugs will not show similar extent of toxicity in all your cell lines. For that reason you need to select the best one upon screening and should carry on to do more work on that particular cell line.
Different cell lines respond in various ways to the antitumor reagent.
In Photodynamic Therapy (PDT) is the same and also in antimicrobial and antifungal activity. A tested photosensitizer or drug will offer different results from excellent to poor function of the type of the cells. For example, a porphyrin structure that is active for optical nerve cancer might be completely inactive for breast cancer.
You have also to vary concentrations, solvents, the administration, the laser power (PDT) for different cell lines.