Tumor is a qualitative mutation and abnormal proliferation of body tissues under the action of internal and external pathogenic factors, forming new tissues that are not coordinated with surrounding tissues. It has abnormal metabolism, which is faster than normal tissues and depletes a lot of nutrition of human body, and at the same time produces a lot of harmful substances to damage the body, causing dysfunction and metabolic disorder of tissues and organs, and destroying normal tissue structure. From the perspective of medical development nowadays, although malignant tumor is no longer a terminal disease, it is still a disease with high mortality rate, which is a great threat to human life. Therefore, the diagnosis, treatment and prevention of tumors are important research topics of modern medicine.
Bladder tumors are the most common malignant tumors in urology, of which 75-80% of bladder tumors are early superficial tumors. Bladder tumors are often multicentric and multiple tumors with a very high recurrence rate. Currently, transurethral electrodesis or laser treatment is more effective for early and mid-stage superficial bladder tumors, but it is not easy to identify in situ cancer that cannot be seen by the naked eye, and the treatment for carpet-like tumors is not uniform and easy to recur, with a recurrence rate of up to 70% within five years after surgery.
Photodynamic therapy (PDT) was introduced in the 1980s and has been rapidly developed in recent years as a new technology for tumor prevention and treatment, which is another new tumor therapy under research and development after the traditional treatments such as surgery, radiotherapy, chemotherapy and immunotherapy. In the past two decades, photodynamic therapy (PDT) has become one of the most active research fields in the world of tumor prevention and treatment science. In many developed countries such as Europe, America and Japan, photodynamic therapy as a new technology for tumor treatment has been reviewed and approved by competent government agencies, and has become a new conventional treatment in more and more hospitals, with deepening basic research and increasingly widespread clinical application.
Photodynamic drugs can be selectively distributed to tumor tissues, and after irradiation by blue light with a wavelength of about 400 nm, the malignant parts of bladder mucosa emit red fluorescence, in contrast to the blue fluorescence of normal bladder mucosa. This, on the one hand, helps to detect lesions that are not detected under normal cystoscopy and improves the accuracy of surgical resection. On the other hand, giving 630 nm laser irradiation at this time stimulates the photodynamic drug in the tumor tissue to selectively kill the tumor tissue and destroy the tiny cancer nests scattered outside the main bladder tumor lesion that are not visible to the naked eye, which can greatly reduce the chance of tumor recurrence.
Although thousands of different types of photosensitizers have been studied in the world, many substances can be considered as photosensitizers, and new photosensitizers are being discovered with regularity; however, few can be applied to the clinic, and very few are developed as commercial products. The most widely used photodynamic cancer drugs for domestic and international clinical applications are hematoporphyrin derivatives (HpD) and its isolated component porfimer sodium (trade name Photofrin). Although HpD has been widely used for photodynamic treatment of cancer since the late 1970s around the world, it has not been officially registered as a new drug in foreign countries. In the 1980s, China has transitioned the clinical use of cancer porphyrin (HpD, Beijing), photoporphyrin (HpD, Yangzhou) and cancer photoporphyrin (PSD-007, Shanghai) in bulk mixed porphyrin formulations. Among them, Beijing HpD (later transferred to Chongqing Huading Pharmaceutical, trade name Xipofen) has obtained the national new drug approval number. PSD-007 was approved by the Ministry of Health of the PLA General Logistics Department for transitional clinical trial in 1983.
1.The basic principle of photodynamic therapy for tumor
The basic principle of photodynamic therapy (PDT) is that photodynamic drugs can be selectively distributed and accumulated in tumor tissues after administration, and photochemical reactions occur after excitation by light of specific wavelengths and with the participation of oxygen in biological tissues, forming highly active and short-lived monomorphic oxygen and other free radicals. This process leads to local vascular occlusion, cellular destruction, and ultimately tumor cell death, thus achieving the therapeutic goal.
The mechanism of action of PDT for tumor treatment is very complicated, in summary, it includes the direct damage effect of photodynamic effect on tumor cells, the destruction of microvessels in tumor causing tumor cells hypoxia, the change of local and systemic immune response, etc. Tumor cell death is the result of many effects combined.
2.Treatment characteristics of photodynamic therapy for tumor
1.High selectivity
The main target of photodynamic therapy is the diseased tissues in the illuminated area, and the damage to the normal tissues around the lesion is slight, which is difficult to be achieved by many other therapeutic means.
2.Minimally invasive
The treatment does not require surgery, the main part only needs to cooperate with endoscopy or other interventional techniques to guide the laser deep into the body for treatment, the treatment takes a short time, avoiding the trauma and pain caused by surgery.
3.Effective treatment
Since the treatment process is based on the strong drug localization effect, the photochemical effect can be produced on all tumors and cancer cells containing photosensitizers, and can enhance the immune system of the body to resist tumors at the same time, so the treatment is more complete and the recurrence rate is low, and most early cancers can be cured.
4.Low toxicity
Except for preventable phototoxic reactions, it has almost no effect on hematopoiesis, immunity and organ functions of the body.
5.Good applicability
It is effective for different cell types of cancer tissues and has a wide range of applicability; while the sensitivity of different cell types of cancer tissues to radiotherapy and chemotherapy can vary greatly and the application is restricted.
6.Repeatable treatment
Cancer cells are not resistant to photosensitive drugs, and patients will not have more toxic reactions due to multiple photodynamic treatments, so treatment can be repeated.
7.Can be palliative treatment
For patients with advanced tumor, or tumor patients who cannot receive surgery due to advanced age, cardiopulmonary, hepatic and renal insufficiency and hemophilia, photodynamic therapy is a palliative treatment that can effectively reduce pain, improve quality of life and prolong life.
8.It can improve the efficacy in cooperation with surgery
For some tumors, surgical resection first and then photodynamic therapy can further eliminate residual cancer cells, reduce the chance of recurrence and improve the thoroughness of surgery; for some other tumors, it is possible to do photodynamic therapy first to make the tumor shrink and then resect, which can expand the indications of surgery and improve the success rate of surgery.
9.It can eliminate the hidden tumor lesions
Clinically, some tumors, such as bladder metastatic cell carcinoma, may have scattered microscopic cancer nests that are not visible to the naked eye outside the main lesion, and conventional treatment means can do nothing about it.