Cervical cancer is the fourth leading cause of cancer-related deaths in women worldwide, with an estimated 604,000 new cases and 342,000 deaths in 2020 [1]. According to a report on HPV-related diseases in China, there were nearly 110,000 new cases of cervical cancer and about 59,000 deaths among Chinese women in 2020, and the incidence of cervical cancer is increasing each year and becoming more prevalent in younger age groups [2]. The occurrence and development of cervical cancer is a continuous process. Cervical carcinoma is preceded by a long period of cervical intraepithelial neoplasia (CIN). The classification of CIN is based on the cellular characteristics to distinguish the level of dysplasia, which is divided into CIN I, mild dysplasia, CIN II, moderate dysplasia, and CIN III, severe dysplasia and carcinoma in situ (CIS) [3, 4].

CIN I is the manifestation of transient high-risk HPV infection, however, 30% of lesions will persist, about 10% of lesions will progress to high-grade squamous intraepithelial lesions (HSIL) within 2 years, and 5% will progress to invasive carcinoma, which is life-threatening [5, 6]. Therefore, treatment for persistent CIN I is an important link to prevent cervical cancer. Although observation and follow-up are recommended for CIN I, facing the risk of persistence or progression of nearly 40% of cervical CIN I, most women refuse observation due to psychological pressure and strongly require active treatment. Women with CIN I persisting for two years can be treated with excision or ablation [6]. CIN II and CIN III are commonly treated either with ablation or excision to remove abnormal epithelial cells. Traditional treatments for CIN II and CIN III include resection therapy, such as loop electrosurgical resection procedures (LEEP), cold knife conization (CKC), and laser conization biopsy. The clinical study indicated that the cure rate for these treatments could reach 90–98% [7]. However, excision invades the surrounding normal tissue, resulting in cervical insufficiency, an increased rate of spontaneous abortion, and other adverse complications [8]. CO2 laser is a physical ablation therapy that vaporizes and carbonizes the lesion tissue by thermal effect and promotes the regeneration of squamous epithelium, which is used in the treatment of cervical epithelial lesions. CO2 laser under colposcope has the advantages of clear vision, precise operation, fewer side effects and simple operation [9, 10]. PDT has also the similar advantages [9, 10].

Photodynamic therapy (PDT) is a novel, non-invasive, and highly selective therapeutic method that has been widely used to treat various cutaneous disorders and non-melanoma skin tumors [11]. In the process of PDT, a photosensitizer is selectively concentrated in the diseased cells and tissues. Then, under the influence of light at a specific wavelength and oxygen, singlet oxygen and reactive oxygen species are produced, which are cytotoxic and can, directly and indirectly, kill diseased cells. 5-aminolevulinic acid (ALA) is a new type of second-generation photosensitizer that has been used as a promising therapeutic agent for cancer treatment in clinical practice [12]. ALA-PDT is effective in treating CIN, vulva intraepithelial neoplasia (VIN), vaginal intraepithelial neoplasia (VaIN), condyloma acuminatum (CA), and other reproductive tract diseases [13].

This study aims to evaluate the efficacy and safety of ALA-PDT for different grades of CIN in women of childbearing age and to explore the risk factors affecting the efficacy of 5-ALA PDT.