Uterine cervical cancer is the second most common type of cancer in females globally (1). According to the Globocan project, the disease has one of the greatest incidences of female mortalities, despite the effective screening system (2). Since cervical cancer is accepted as a radiosensitive tumor, ionizing radiation is the most frequently used treatment modality against the disease. Therefore, cellular radiosensitivity is a long-term research focus in the field of radiation oncology and biology as it has a clear effect on the outcome of therapy (3). The tumors, however, are not equally sensitive to radiation (4).

Traditionally, radioresistant tumors have been mainly designated from the histopathological viewpoint (5). Glassy cell carcinoma and small cell carcinoma, including neuroendocrine tumors of the cervix, are generally regarded as radioresistant tumors. These specific histological types, however, are rather rare in cervical neoplasms. Furthermore, there may be significant variation in radiosensitivity even within the same histological type. Thus, tumor histology may not be a crucial determinant of radiosensitivity.

The initial damage should be a major determinant of cell radiosensitivity (6). By contrast, flow cytometry (FC) is a technique for the rapid analysis of DNA content, phenotype expression and the sorting of cells for further studies. FC allows quantitative measurements on single cells or cellular constituents at an extremely high speed rate. It is also feasible to monitor the effects of radiation on the cell cycle distribution following DNA staining of mammalian cells (7, 8). Since the formation of DNA double-strand breaks is considered to be critical for the cytocidal effect of radiation therapy (9–12), identifying the underlying molecular processes that results in radioresistance may lead to novel radiosensitising strategies.

A newly developed microscope-based laser scanning cytometer (LSC) offers a number of advantages over FC (13, 14). LSC can assess the DNA index (DI) in hypocellular materials, even on cytological smear slides (15).

Cell necrobiology incorporates the life processes associated with morphological, biochemical and molecular changes that predispose, precede and accompany cell death, and assess the consequences and tissue response to cell death (16). The aim of the present study was to discern the radiation-induced initial damage that leads to cancer cell death by necrobiological observation, including cytological morphology and LSC.

Although ionizing radiotherapy is a key strategy and has >80 years history in the treatment of cervical cancer, the crucial determinant of radiosensitivity of the tumor remains unknown (3, 4, 19). Thus, understanding how to identify the treatment-induced initial damage of cancer cells is essential for further therapeutic plans in cancer therapy. An assay with the ability to predict the radiosensitivity of tumors may provide a useful tool for the further individualization of radiotherapy of cancer patients (20). The prognostic significance of the fraction of survival following 2 Gy of radiation (SF2) is crucial in the treatment of head and neck cancer (21). However, the methods to determine SF2 can take ≤4 weeks and are therefore not clinically practical.

To improve the treatment strategy, the early evaluation of therapeutic responses should be performed. The current response criteria, including that of the UICC, are only used for the evaluation of the treatment results. Radiation damages can be observed as cellular degeneration by cytology. However, these are late events in the treatment course. The importance of a more prompt evaluation is critical with regards to clinical decision making.

The impacts of radiation on cervical cancer cells resulted in a significant elevation of the DNA content level in six out of seven cases. Radiation causes a division delay dominated by G2 arrest in the cell cycle. The delay is likely a mechanism allowing the cell to repair its DNA damage. Ionizing radiation can also induce polyploidization in a cancer cell line (22). Furthermore, radiation-induced apoptosis is morphologically identified by an increase in cytoplasmic granularity, chromatin condensation, membrane blebbing, cell shrinkage and the formation of distinctive nuclear bodies. These radiation effects should attribute to the change of DNA content.

Currently, there are a number of studies reporting on the concern of the radiation impacts on the molecular structure of cancer cells by novel techniques, including cytometry and LSC, revealing the precise mechanism involved in radiation effects. Despite the notable technical advance in elucidation of the molecular mechanism of the radiation effects, the results obtained remain to be utilized in clinical decision making. Rapid analyses of radiation-induced molecular changes by LSC are promising, although certain changes remain to be resolved, and this can lead to the ‘real-time judgement’ of the radiosensitivity of the tumor, and aid in making a treatment decision in the clinical practice.