Cervical cancer is a highly prevalent and severe life-threatening malignancy among women worldwide. More than 85% of cervical cancer cases take place in developing countries (1). Notably, in China alone, there were approximately 150,700 new cases and 55,700 deaths in 2022 (2). Hence, cervical cancer is a major public health problem affecting women in China. Histologically confirmed cervical HSIL, a precursor to cervical cancer, occurs as a result of persistent HR-HPV infection, has a risk of 20-30% to progress into invasive carcinoma within 10 years (3). Conventionally, managements for cervical HSIL including cold knife conization, laser conization, laser ablation and loop electrosurgical excision procedure (LEEP) (4), which can lead to cervical distortion, excessive destruction of tissue, and subsequent obstetric complications such as preterm labor, premature rupture of amniotic membranes, chorioamnionitis, low birth weight, and increased morbidity in the newborns (5–7). In China, with the gradual liberalization of fertility policies and the younger onset age of the female lower genital tract diseases, there is an increasing demand to protect normal cervical structure and preserve fertility. Therefore, there is a desirable need to explore effective conservative treatments with minimal damage and fewer adverse reactions for managing cervical HSIL.

Photodynamic therapy (PDT) is an emerging alternative technique for the treatment of squamous intraepithelial lesions. It works through the interaction of photosensitizing agents, light and oxygen, providing a non-invasive, effective and targeted treatment (8). 5-aminolevulinic acid (5-ALA), as a second-generation photosensitizer, can accumulate in higher concentrations in pathological cells and absorb light of the appropriate wavelength. This initiates the photodynamic reactions and selective destruction of inappropriate tissues (8, 9). In recent years, several studies have reported the satisfactory efficacy and safety of PDT in treating cervical LSIL (10–13). Chinese experts in gynecology and obstetrics unanimously recognized the importance of 5-aminolevulinic acid-based photodynamic therapy and reached a consensus on its clinical application in female lower genital tract diseases in 2022 (14). However, there are insufficient studies evaluating the efficacy of ALA-PDT for patients with cervical HSIL.

Our center, being one of the early adopters of ALA-PDT for treating female lower genital tract disorders, implemented this program in 2019. In this retrospective observational survey, we aimed to investigate the effectiveness and safety of ALA-PDT as a potential option for patients with cervical HSIL, as well as identify factors that impact its efficacy.

Currently, cervical cancer is the fourth most common malignancy in women worldwide, and it is still a major cause of cancer-related death in some of the world’s poorest countries (18). In 2018, the World Health Organization issued a global call for the elimination of cervical cancer as a public health problem (19). The strategies for eliminating cervical cancer included primary prevention via HPV vaccination, secondary prevention via cervical screening, and the third prevention of timely management of precancerous lesions. HSIL of the cervix, which is induced by HR-HPV, is a premalignant disease. In the past, surgical excision using methods like cold knife conization, laser conization/ablation, or LEEP was the gold standard treatment for cervical HSIL (4). Because of young women’s low-acceptance of surgical procedures and the associated complications, as well as their strong desire for complete preservation of cervical tissues, it is imperative to explore a non-invasive and effective method for the management of cervical HSIL. ALA-PDT seems to be a good choice for this specific group of patients.

ALA-PDT involves the selective accumulation of 5-aminolevulinic acid in the CIN tissues (20), which are then illuminated to generate ROS that destroy tumor cells by inducing apoptosis and necrosis. The success of the process relies on three key points: oxygen-induced activation of photosensitizer, appropriate utilization of visible light, and proper selection of the photosensitizer (21). This process is highly tissue selective, non -invasive, and carries a low risk of severe complications, making it an ideal method for treating cervical HSIL, especially for young women. Compared to traditional surgical excisions, ALA-PDT is characterized by elimination of precancerous lesions and potential HPV infection (22) without causing damage to the normal anatomy.

Our study showed that ALA-PDT was highly effective in treating a cervical HSIL, leading to a complete remission rate of 65% at 3 months after completion of ALA-PDT. Furthermore, with an extended observation period, the complete remission rate could reach as high as 82.5% at 12 months after the completion of ALA-PDT. These findings are consistent with previous studies. Wu et al. reported a histological complete remission rate of 77.78% for CIN II after PDT at 12-month follow-up (23). Tang et al. revealed that the cervical HSIL complete remission rate after PDT was 88.9%, 92.5% at 6-months,12-months follow-up respectively (24). Qu et al. found that the total lesion regression rate of cervical HSIL after PDT was 89.58% at 3-months follow-up (25). Hu et al. reported that the disappearance rate of cervical HSIL after PDT was 81.82%, 90.91% at 3-month,6-month follow-up respectively (26). Although the above studies reported a satisfactory efficacy of PDT for HSIL treatment, there are still some limitations. The application of ALA-PDT in cervical HSIL is still in the initial exploration stage, and the included cases in the above studies were limited, which might limit the generalizability and robustness of the conclusions. Further studies with high-level of evidence, such as multicenter, large-sample, randomized controlled clinical trials, are necessary to be conducted to validate our findings. Additionally, it should be noted that our study primarily focused on patients with CIN II, only 2 patients with CIN III were included. One patient was diagnosed with CIN II-III and responded positively to ALA-PDT treatment, showing normal cervical cytological and HPV test results after three months. Conversely, the second patient, diagnosed with CIN III, did not benefit from this therapy and instead achieved recovery through LEEP. This discrepancy in treatment efficacy may be attributed to the greater lesion depth associated with CIN III, which renders non-invasive treatments such as ALA-PDT less effective than they are for CIN I and CIN II cases. Due to the lack of sufficient data, we cannot make some rigorous suggestions for CIN III patients. Further research including larger subjects is needed to demonstrate the effectiveness of PDT for patients with CIN III.

There is no consensus on the follow-up strategy after PDT. In our study, we evaluate the combination of HPV genotyping and cervical cytological results as an initial evaluation at the 3-month follow-up. Cases were then triaged according to the results. The stratification protocol in our study was to immediately refer to colposcopy-guided biopsy if the cytologic result was worse than ASC-US at the 3-month follow-up. If the cervical cytological result was ASC-US and/or there was HR-HPV infection, observation could continue with repeated cervical screening at 6-months follow-up. We designed this stratification protocol based on previous studies reporting that PDT could enhance local and systemic immunity, which plays a crucial role in clearing lesions (27–29). Therefore, we have implemented a relatively conservative observation protocol for patients with either cytology result ASC-US or HR -HPV infection 3 months after PDT treatment. We hypothesized that the activated immune response by PDT would have a long-term effect on the clearance of lesions or HR-HPV, thus ensuring the safety of this group of patients. In our study, 8 cases that met this criterion(either cytologic result ASC-US and/or HR-HPV infection). Among them, 6 patients returned to normal cytology and negative HPV within 1 year by observation, one patient regressed from CIN II to CINI, and one patient persisted in CIN II. None of the patients had a history of disease progression during the course of observation. Therefore, we consider our triage program to be reasonable.

In our study of single factor analysis, we found that cervical canal involvement, multiple lesions and infection with more than one species of HR-HPV can cause persistent viral infection at the 3-month follow-up after ALA-PDT treatment. However, multiple linear regression analysis revealed that only cervical canal involvement was an independent risk factor. These findings suggest that the effects of multiple lesions and HR-HPV species are secondary to the difference in cervical canal involvement. Consequently, even if a patient has numerous lesions and HR-HPV infection, if there is no disease in the cervical canal, ALA-PDT can effectively eliminate her HR-HPV infection. We infer that the reason maybe the optical fiber is not as efficient as the intravaginal light scattering cylindrical head. Thus, we recommend to prolong the time of irradiation by the optical fiber for patients with cervical canal lesions. The underlying association between cervical involvement and persistent HR-HPV infection requires further research. It is important to monitor women with persistence of HR-HPV infection who have underwent PDT therapy as it greatly impacts the prognosis. Our findings emphasize the need to pay extra attention to the patients with cervical involvement.

During the treatment of the 40 patients with ALA-PDT, there were no severe adverse reactions. A few patients presented with discomfort symptoms, such as burning sensations, slight pain, slight discomforts in the lower abdomen and increased vaginal discharge. These adverse reactions were bearable and were relieved within a few days after treatment, indicating the safety of ALA-PDT.

During our research, patients underwent a treatment regimen of ALA- PDT with a frequency of once per week, typically completing six sessions. The entire course of treatment spanned approximately 7 weeks to 2 months, which is notably longer than the single-session requirement of other non-invasive therapies such as laser, cryotherapy, and thermal ablation. Despite the extended duration, ALA-PDT offers the advantage of being less painful in comparison to these alternatives. Moreover, the satisfactory outcomes observed in this study can be partly attributed to the regularity of the ALA-PDT treatment sessions.

Non-invasive physical plasma (NIPP), which inhibit pathological cell growth through rapid and transient DNA damage, is another emerging approach for cervical precancerous lesions. Like ALA-PDT, NIPP is a tissue-preserving and easy-to-apply method, which can be performed in outpatient settings without the need for local or general anesthesia and is more cost-effective than ALA-PDT. Previous studies have reported that the complete remission rate of NIPP to CINI/II reached 86.2% -95% at 3-6 months after treatment (30, 31). However, these studies were single arm prospective studies and included a small sample size. Further studies are expected to include larger population and reveal the efficacy of NIPP in CINII/III patients. NIPP may be an underlying alternative to ALA-PDT for the treatment of cervical HSIL.

1. ALA-PDT is a highly effective, non-invasive, and safe therapeutic intervention for cervical HSIL. Compare to surgical procedures, it has the advantage of preserving the structural and functional integrity of the cervix. Therefore, it is an optimal choice for young women with cervical HSIL who have fertility requirements. 2. We suggest continuous observation instead of performing a colposcopy-guided biopsy in patients who have either a cervical cytological result of ASU-US and/or a HR-HPV infection at 3-month follow-up after ALA-PDT therapy. 3. Cervical canal involvement is an independent risk factor for persistent HR-HPV infection at the 3-month follow-up after PDT treatment.

The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding authors.

The studies involving humans were approved by Ethics Committee of Hangzhou First people’s Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

JQ: Writing – review & editing, Writing – original draft, Formal analysis, Data curation, Conceptualization. YW: Writing – review & editing, Supervision, Investigation. GW: Writing – review & editing, Resources, Data curation. JL: Writing – review & editing, Resources. LS: Writing – review & editing, Supervision, Conceptualization. SX: Writing – review & editing, Software, Methodology, Formal analysis, Conceptualization.