MR Imaging Grading System for Skull Base Chordoma

Magnetic resonance imaging signal characteristics associated with prognosis of skull base chordoma after gamma knife radiosurgery

OBJECTIVE

To investigate the association between the magnetic resonance imaging (MRI) signal characteristics of skull base chordoma and radiosurgical outcomes.

METHODS

Twenty-four patients with skull base chordomas treated with Gamma Knife radiosurgery (GKRS) after previous surgical resection were retrospectively (2001-2021) examined. Pre-GKRS MRIs were analyzed for R_T2 (tumor-to-brainstem signal intensity ratio on T2-weighted imaging), R_CE (tumor-to-brainstem signal intensity ratio on contrast-enhanced T1-weighted imaging), and mean apparent diffusion coefficient (ADC). Correlations of the parameters with patient survival and local tumor progression were made by using Cox regression and Kaplan-Meier analyses.

RESULTS

During a median follow-up of 46 months after GKRS, 9 patients died with significantly more local tumor progression events (median number: 2 vs 0, P = .012) than did 15 alive patients. On multivariable analysis, higher mean ADC was associated with longer patient survival (P = .016) after GKRS. The actuarial 5-year overall survival rates were 88.9% versus 54.7% for chordomas with an ADC of ≥ 1270 × 10^-6 mm²/s versus < 1270 × 10^-6 mm²/s. R_T2 < 1.5 (P = .038) and R_CE > 1.57 (P = .022) were associated with a lower probability of local tumor control.

CONCLUSION

Lower mean ADC values are associated with shorter patient survival in skull base chordomas after GKRS. Diffusion-weighted imaging may help in GKRS planning and outcome prediction for these patients.

Differences in stromal component of chordoma are associated with contrast enhancement in MRI and differential gene expression in RNA sequencing

Chordoma is a malignant bone neoplasm demonstrating notochordal differentiation and it frequently involves axial skeleton. Most of chordomas are conventional type with varying amount of myxoid stroma. Previously known prognostic factors for conventional chordoma are not specific for chordoma: old age, metastasis, tumor extent, and respectability. Here, we aimed to investigate the histologic, radiologic, and transcriptomic differences in conventional chordoma based on the stromal component. A total of 45 patients diagnosed with conventional chordoma were selected between May 2011 and March 2020 from a single institution. Electronic medical records, pathology slides, and pretreatment magnetic resonance imaging (MRI) scans were reviewed. Of the 45 patients, ten cases (4 stroma-rich and 6 stroma-poor tumor) were selected for RNA sequencing, and available cases in the remainder were used for measuring target gene mRNA expression with qPCR for validation. Differential gene expression and gene set analysis were performed. Based on histologic evaluation, there were 25 (55.6%) stroma-rich and 20 (44.4%) stroma-poor cases. No clinical differences were found between the two groups. Radiologically, stroma-rich chordomas showed significant signal enhancement on MRI (72.4% vs 27.6%, p = 0.002). Upregulated genes in stroma-rich chordomas were cartilage-, collagen/extracellular matrix-, and tumor metastasis/progression-associated genes. Contrarily, tumor suppressor genes were downregulated in stroma-rich chordomas. On survival analysis, Kaplan–Meier plot was separated that showed inferior outcome of stroma-rich group, although statistically insignificant. In conclusion, the abundant stromal component of conventional chordoma enhanced well on MRI and possibly contributed to the biological aggressiveness that supported by transcriptomic characteristics. Further extensive investigation regarding radiologic-pathologic-transcriptomic correlation in conventional chordoma in a larger cohort could verify additional clinical significance.

Chordoma: To know means to recognize

Chordoma is a rare type of bone cancer characterized by its locally aggressive and destructive behavior. Chordoma is located in one of the three primary regions: skull base/clivus, sacrum or mobile spine. Chordoma grows slowly, therefore its insidious onset leads to delayed diagnosis, accounting for the low survival rates. Treatment centers around successful en bloc resection with negative margins, though, considering the anatomically constrained site of growth, it frequently requires adjuvant radiotherapy. This article analyzes the existing literature with the aim to provide a better insight in the current state of research in chordoma classification, characteristics, and management.

MRI enhancement patterns in 28 cases of clival chordomas

Clival chordomas are classically thought of as locally aggressive tumors of the skull base and differentiate themselves from their benign counterparts by demonstrating moderate to marked contrast enhancement, reported as 95-100% in prior studies. The purpose of this review was to evaluate the imaging characteristics of lesions from a single institution classified as clival chordomas with an emphasis of highlighting lesions that do not follow the prevalent current description for chordoma. We searched our institutional databases for all patients with pathologically proven clival chordomas from 1997 to 2017 who had pre-operative imaging available. The images were evaluated for degree of contrast enhancement, MRI signal characteristics, osseous involvement, location, aggressiveness of appearance, and presence of calcifications. 28 cases were identified that had preoperative imaging available for review. Over half of the patients demonstrated either no/minimal (11/28, 39%) or mild enhancement (7/28, 25%). The remaining cases demonstrated moderate (4/28, 14%) and marked enhancement (6/28, 21%). The 4 lesions measuring less than 20 mm all had mild to minimal/no enhancement and lacked aggressive features on CT. Our experience finds that over half (64%) of clival chordomas will demonstrate mild or no enhancement at all. These findings suggest that the lack of MRI contrast enhancement should not be synonymous with a benign clival mass.

Tumor Growth Rate as a New Predictor of Progression-Free Survival After Chordoma Surgery

BACKGROUND

Currently, different postoperative predictors of chordoma recurrence have been identified. Tumor growth rate (TGR) is an image-based calculation that provides quantitative information of tumor's volume changing over time and has been shown to predict progression-free survival (PFS) in other tumor types.

OBJECTIVE

To explore the usefulness of TGR as a new preoperative radiological marker for chordoma recurrence.

METHODS

A retrospective single-institution study was carried out including patients reflecting these criteria: confirmed diagnosis of chordoma on pathological analysis, no history of previous radiation, and at least 2 preoperative thin-slice magnetic resonance images available to measure TGR. TGR was calculated for all patients, showing the percentage change in tumor size over 1 mo.

RESULTS

A total of 32 patients were retained for analysis. Patients with a TGR ≥ 10.12%/m had a statistically significantly lower mean PFS (P < .0001). TGR ≥ 10.12%/m (odds ratio = 26, P = .001) was observed more frequently in recurrent chordoma. In a subgroup analysis, we found that the association of Ki-67 labeling index ≥ 6% and TGR ≥ 10.12%/m was correlated with recurrence (P = .0008).

CONCLUSION

TGR may be considered as a preoperative radiological indicator of tumor proliferation and seems to preoperatively identify more aggressive tumors with a higher tendency to recur. Our findings suggest that the therapeutic strategy and clinical-radiological follow-up of patients with chordoma can be adapted also according to this new parameter.

Peri-operative prognostic factors for primary skull base chordomas: results from a single-center cohort

BACKGROUND

Skull base chordomas (SBC) are rare malignant tumors and few factors have been found to be reliable markers for clinical decision making and survival prognostication. The aim of the present work was to identify specific prognostic factors potentially useful for the management of SBC patients.

METHODS

A retrospective review of all the patients diagnosed and treated for SBC at the Fondazione IRCCS Istituto Neurologico "Carlo Besta" between January 1992 and December 2017 has been performed. Survival analysis was performed and a logistic regression model was used. Statistically significant predictors were rated based on their log odds in order to preliminarily build a personalized grading scale-the Peri-Operative Chordoma Scale (POCS).

RESULTS

Fifty-nine primary chordoma patients were included. The average follow-up from the first treatment was 82.6 months (95% CI, 65.5-99.7). POCS was built over PFS and MR contrast enhancement (intense vs mild/no, value 4), preoperative motor deficit (yes vs no, value 3), and the development of any postoperative complications (yes vs no, value 2). POCS ranges between 0 and 9, with higher scores being associated with reduced likelihood of survival and progression-free state.

CONCLUSIONS

Our results show that preoperative clinical symptoms (motor deficits), surgical features (extent of tumor resection and surgeon's experience), development of postoperative complications, and KPS decline represent significant prognostic factors. The degree of MR contrast enhancement significantly correlated to both OS and PFS. We also preliminarily developed the POCS as a prognostic grading scale which may help neurosurgeons in the personalized management of patients undergoing potential adjuvant therapies.

Radiomics and Dosiomics for Predicting Local Control after Carbon-Ion Radiotherapy in Skull-Base Chordoma

Skull-base chordoma (SBC) can be treated with carbon ion radiotherapy (CIRT) to improve local control (LC). The study aimed to explore the role of multi-parametric radiomic, dosiomic and clinical features as prognostic factors for LC in SBC patients undergoing CIRT. Before CIRT, 57 patients underwent MR and CT imaging, from which tumour contours and dose maps were obtained. MRI and CT-based radiomic, and dosiomic features were selected and fed to two survival models, singularly or by combining them with clinical factors. Adverse LC was given by in-field recurrence or tumour progression. The dataset was split in development and test sets and the models' performance evaluated using the concordance index (C-index). Patients were then assigned a low- or high-risk score. Survival curves were estimated, and risk groups compared through log-rank tests (after Bonferroni correction α = 0.0083). The best performing models were built on features describing tumour shape and dosiomic heterogeneity (median/interquartile range validation C-index: 0.80/024 and 0.79/0.26), followed by combined (0.73/0.30 and 0.75/0.27) and CT-based models (0.77/0.24 and 0.64/0.28). Dosiomic and combined models could consistently stratify patients in two significantly different groups. Dosiomic and multi-parametric radiomic features showed to be promising prognostic factors for LC in SBC treated with CIRT.

Magnetic resonance imaging of the hypothalamo-pituitary region

The diagnosis and management of mass lesions in the sellar and parasellar areas remain challenging. When approaching patients with possible sellar or hypothalamic masses, it is important not only to focus on imaging but also detect possible pituitary hormone deficits or excess, in order to establish an appropriate diagnosis and initiate treatment. The imaging modalities used to characterize hypothalamic and pituitary lesions have significantly evolved over the course of the past several years. Computed tomography (CT) and CT angiography play a major role in detecting various sellar lesions, especially in patients who have contraindications to magnetic resonance imaging (MRI) and can also yield important information for surgical planning. However, MRI has become the gold standard for the detection and characterization of hypothalamic and pituitary tumors, infections, cystic, or vascular lesions. Indeed, the imaging characteristics of hypothalamic and sellar lesions can help narrow down the differential diagnosis preoperatively. In addition, MRI can help establish the relationship of mass lesions to surrounding structures. A pituitary MRI examination should be obtained if there is concern for mass effect (including visual loss, ophthalmoplegia, headache) or if there is clinical suspicion and laboratory evidence of either hypopituitarism or pituitary hormone excess. The information obtained from MRI images also provides us with assistance in planning surgery. Using intraoperative MRI can be very helpful in assessing the adequacy of tumor resection. In addition, MRI images yield reliable data that allow for noninvasive monitoring of patients postoperatively.

MRI Signal Intensity and Electron Ultrastructure Classification Predict the Long-Term Outcome of Skull Base Chordomas

BACKGROUND AND PURPOSE

MR imaging is a useful and widely used evaluation for chordomas. Prior studies have classified chordomas into cell-dense type and matrix-rich type according to the ultrastructural features. However, the relationship between the MR imaging signal intensity and ultrastructural classification is unknown. We hypothesized that MR imaging signal intensity may predict both tumor ultrastructural classification and prognosis.

MATERIALS AND METHODS

Seventy-nine patients with skull base chordomas who underwent 95 operations were included in this retrospective single-center series. Preoperative tumor-to-pons MR imaging signal intensity ratios were calculated and designated as ratio on T1 FLAIR sequence (R_T1), ratio on T2 sequence (R_T2), and ratio on enhanced T1 FLAIR sequence (R_EN), respectively. We assessed the relationships among signal intensity ratios, ultrastructural classification, and survival.

RESULTS

Compared with the matrix-rich type group, the cell-dense type chordomas showed lower R_T2 (cell-dense type: 1.90 ± 0.38; matrix-rich type: 2.61 ± 0.60 P < .001). The model of predicting cell-dense type based on R_T2 had an area under the curve of 0.83 (95% CI, 0.75-0.92). In patients without radiation therapy, both progression-free survival (P = .003) and overall survival (P = .002) were longer in the matrix-rich type group than in the cell-dense type group. R_EN was a risk factor for progression-free survival (hazard ratio = 10.24; 95% CI, 1.73-60.79); R_T2 was a protective factor for overall survival (hazard ratio  = 0.33; 95% CI, 0.12-0.87); and R_EN was a risk factor for overall survival (hazard ratio = 4.76; 95% CI, 1.51-15.01).

CONCLUSIONS

The difference in MR imaging signal intensity in chordomas can be explained by electron microscopic features. Both signal intensity ratios and electron microscopic features may be prognostic factors.

Natural Growth Dynamics of Untreated Skull Base Chordomas In Vivo

OBJECTIVE

To study the natural growth dynamics of skull base chordomas.

METHODS

A retrospective study of skull base chordomas was performed. Patients with ≥2 preoperative magnetic resonance (MR) images and with pathologically confirmed chordomas were enrolled. All clinical data and MR images were studied.

RESULTS

Twenty-one patients with pathologically confirmed skull base chordomas were enrolled. The mean volume of the tumors at diagnosis was 19.9 ± 17.0 cm³, with a mean interval examination period of 22.4 ± 26.1 (range, 3-113) months. The mean tumor volume change was approximately 15.4 ± 16.3 cm³. The mean specific growth rate was 8% ± 9% per month, and the mean specific growth volume was 0.8 ± 0.7 cm³ per month. The tumor MR signal index grade, female gender, no dura mater breakthrough, endophytic type, small tumors, and soft tumor texture were related to a higher tumor growth rate (P < 0.05), and small tumors showed the greatest growth rate compared with the middle-sized and large tumors. Curve estimation was performed using a power function (R² = 0.545).

CONCLUSIONS

The skull base chordoma is a slow-growing tumor. The cases involving characteristics of female gender, endophytic type, small tumor size, and MR grade 3 showed a higher growth rate.

High expression of survivin independently correlates with tumor progression and mortality in patients with skull base chordomas

OBJECTIVE

The object of this study was to clarify the expression characteristics and prognostic value of survivin in skull base chordomas.

METHODS

In this retrospective study, the authors measured the expression of survivin at the mRNA level in 81 samples from 71 patients diagnosed with skull base chordomas at their hospital in the period from July 2005 to January 2015. Clinical data collection, follow-up, and survival analyses were performed, and correlations were analyzed.

RESULTS

Of the 71 patients, 50 had primary chordomas with a mean survivin expression level of 1.09; the other 21 patients had recurrent chordomas with a mean survivin expression level of 2.57, which was 2.36 times higher than the level in the primary chordoma patients (p < 0.001, Mann-Whitney U-test). In addition, an analysis of 18 paired samples derived from 9 patients showed that the expression level of survivin was 2.62 times higher in recurrent tumors than in primary tumors (p = 0.002, paired t-test). The Spearman rank correlation coefficient method showed that the expression level of survivin was positively correlated with the mean ratio of tumor signal intensity to the signal intensity of surrounding brainstem on T1-weighted sequences (RT1; rs = 0.274, p = 0.021) and was negatively correlated with the mean ratio of tumor signal intensity to the signal intensity of surrounding brainstem on T2-weighted sequences (RT2; rs = -0.389, p = 0.001). A multivariate Cox proportional-hazards model suggested that pathology (p = 0.041), survivin expression level (p = 0.018), preoperative Karnofsky Performance Status (KPS; p = 0.012), and treatment history (p = 0.009) were independent prognostic factors for tumor progression. Survivin expression level (p = 0.008), preoperative KPS (p = 0.019), tumor diameter (p = 0.027), and intraoperative blood loss (p = 0.015) were independent prognostic factors for death.

CONCLUSIONS

Survivin expression level and preoperative KPS were independent significant prognostic factors for tumor progression and death in skull base chordoma patients. Recurrent skull base chordomas and chordomas with high RT1 and low RT2 were likely to have high survivin expression. Other independent risk factors related to tumor progression included conventional pathology and treatment history, whereas additional mortality-related risk factors included larger tumor diameter and greater intraoperative blood loss.

Radiomic signature: A novel magnetic resonance imaging-based prognostic biomarker in patients with skull base chordoma

BACKGROUND AND PURPOSE

We used radiomic analysis to establish a radiomic signature based on anatomical magnetic resonance imaging (MRI) sequences and explore its effectiveness as a novel prognostic biomarker for skull base chordoma (SBC).

MATERIALS AND METHODS

In this retrospective study, radiomic analysis was performed using preoperative axial T₁ FLAIR, T₂-weighted, and enhanced T₁ FLAIR from a single hospital. The primary clinical endpoint was progression-free survival. A total of 1860 3-D radiomic features were extracted from manually segmented region of interest. Pearson correlation coefficient was used for feature dimensional reduction and a ridge regression-based Cox proportional hazards model was used to determine a radiomic signature. Afterwards, radiomic signature and nine other potential prognostic factors, including age, gender, histological subtype, dural invasion, blood supply, adjuvant radiotherapy, extent of resection, preoperative KPS, and postoperative KPS were analyzed to build a radiomic nomogram and a clinical model. Finally, we compared the nomogram with each prognostic factor/model by DeLong's test.

RESULTS

A total of 148 SBC patients were enrolled, including 64 with disease progression. The median follow-up time was 52 months (range 4-122 months). The Harrell's concordance index of the radiomic signature was 0.745 (95% CI, 0.709-0.781) for the validation cohort, and its discrimination accuracy in predicting progression risk at 5 years in the same cohort was 82.4% (95% CI, 72.6-89.7%).

CONCLUSIONS

The radiomics is a low-cost, non-invasive method to predict SBC prognosis preoperatively. Radiomic signature is a potential prognostic biomarker that may allow the individualized evaluation of patients with SBC.

Long and Very-Long-Chain Ceramides Correlate with A More Aggressive Behavior in Skull Base Chordoma Patients

BACKGROUND

Skull base chordomas are rare tumors arising from notochord. Sphingolipids analysis is a promising approach in molecular oncology, and it has never been applied in chordomas. Our aim is to investigate chordoma behavior and the role of ceramides.

METHODS

Ceramides were extracted and evaluated by liquid chromatography and mass spectrometry in a cohort of patients with a skull base chordoma. Clinical data were also collected and correlated with ceramide levels. Linear regression and correlation analyses were conducted.

RESULTS

Analyzing the association between ceramides level and MIB-1, total ceramides and dihydroceramides showed a strong association (r = 0.7257 and r = 0.6733, respectively) with MIB-1 staining (p = 0.0033 and p = 0.0083, respectively). Among the single ceramide species, Cer C24:1 (r = 0.8814, p ≤ 0.0001), DHCer C24:1 (r = 0.8429, p = 0.0002) and DHCer C18:0 (r = 0.9426, p ≤ 0.0001) showed a significant correlation with MIB-1.

CONCLUSION

Our lipid analysis showed ceramides to be promising tumoral biomarkers in skull base chordomas. Long- and very-long-chain ceramides, such as Cer C24:1 and DHCer C24:1, may be related to a prolonged tumor survival and aggressiveness, and the understanding of their effective biological role will hopefully shed light on the mechanisms of chordoma radio-resistance, tendency to recur, and use of agents targeting ceramide metabolism.

Radiomic analysis of multiparametric magnetic resonance imaging for differentiating skull base chordoma and chondrosarcoma

PURPOSE

Patients with skull base chordoma and chondrosarcoma have different prognoses and are not readily differentiated preoperatively on imaging. Multiparametric magnetic resonance imaging (MRI) is a routine diagnostic tool that can noninvasively characterize the salient characteristics of tumors. In the present study, we developed and validated a preoperative multiparametric MRI-based radiomic signature for differentiating these tumors.

METHOD

This retrospective study enrolled 210 patients and consecutively divided them into the primary and validation cohorts. A total of 1941 radiomic features were acquired from preoperative T1-weighted imaging, T2-weighted imaging and contrast-enhanced T1-weighted imaging for each patient. The most discriminative features were selected by minimum-redundancy maximum-relevancy and recursive feature elimination algorithms in the primary cohort. The multiparametric and single-sequence MRI signatures were constructed with the selected features using a support vector machine model in the primary cohort. The ability of the novel radiomic signatures to differentiate chordoma from chondrosarcoma were assessed using receiver operating characteristic curve analysis in the validation cohort.

RESULTS

The multiparametric radiomic signature, which consisted of 11 selected features, reached an area under the receiver operating characteristic curve of 0.9745 and 0.8720 in the primary and validation cohorts, respectively. Moreover, compared with each single-sequence MRI signature, the multiparametric radiomic signature exhibited better classification performance with significant improvement (p <  0.05, Delong's test) in the primary cohorts.

CONCLUSION

By combining features from three MRI sequences, the multiparametric radiomics signature can accurately and robustly differentiate skull base chordoma from chondrosarcoma.

Prognostic Implications of Gadolinium Enhancement of Skull Base Chordomas

BACKGROUND AND PURPOSE

Skull base chordomas often demonstrate variable MR imaging characteristics, and there has been limited prior research investigating the potential clinical relevance of this variability. The purpose of this retrospective study was to assess the prognostic implications of signal intensity on standard imaging techniques for the biologic behavior of skull base chordomas.

MATERIALS AND METHODS

Medical records were retrospectively reviewed for 22 patients with pathologically confirmed skull base chordomas. Clinical data were recorded, including the degree of surgical resection, the presence or absence of radiation therapy, and time to progression/recurrence of the tumor or time without progression/recurrence of the tumor following initial treatment. Pretreatment imaging was reviewed for the presence or absence of enhancement and the T2 signal characteristics. Tumor-to-brain stem signal intensity ratios on T2, precontrast T1, and postcontrast T1 spin-echo sequences were also calculated. Statistical analysis was then performed to assess correlations between imaging characteristics and tumor progression/recurrence.

RESULTS

Progression/recurrence of skull base chordomas was seen following surgical resection in 11 of 14 (78.6%) patients with enhancing tumors and in zero of 8 patients with nonenhancing tumors. There was a statistically significant correlation between skull base chordoma enhancement and subsequent tumor progression/recurrence (P < .001), which remained significant after controlling for differences in treatment strategy (P < .001). There was also a correlation between postcontrast T1 signal intensity (as measured by postcontrast T1 tumor-to-brain stem signal intensity ratios) and recurrence/progression (P = .02). While T2 signal intensity was higher in patients without tumor progression (median tumor-to-brain stem signal intensity ratios on T2 = 2.27) than in those with progression (median tumor-to-brain stem signal intensity ratios on T2 = 1.78), this association was not significant (P = .12).

CONCLUSIONS

Enhancement of skull base chordomas is a risk factor for tumor progression/recurrence following surgical resection.

State-of-the-Art Imaging in Human Chordoma of the Skull Base

Purpose of Review

Chordoma are rare tumours of the axial skeleton which occur most often at the base of the skull and in the sacrum. Although chordoma are generally slow-growing lesions, the recurrence rate is high and the location makes it often difficult to treat. Both computed tomography (CT) and magnetic resonance imaging (MRI) are crucial in the initial diagnosis, treatment planning and post-treatment follow-up.

Recent Findings

Basic MRI and CT characteristics of chordoma were described in the late 1980s and early 1990s. Since then, imaging techniques have evolved with increased resolution and new molecular imaging tools are rapidly evolving. New imaging tools have been developed not only to study anatomy, but also physiologic changes and characterization of tissue and assessment of tumour biology. Recent studies show the uptake of multiple PET tracers in chordoma, which may become an important aspect in the diagnosis, follow-up and personalized therapy.

Summary

This review gives an overview of skull base chordoma histopathology, classic imaging characteristics, radiomics and state-of-the-art imaging techniques that are now emerging in diagnosis, treatment planning and disease monitoring of skull base chordoma.

5-Aminolevulinic acid-based photodynamic therapy of chordoma: In vitro experiments on a human tumor cell line

BACKGROUND

Chordomas are very rare tumors of the skull base and the sacrum. They show infiltrating and destructive growth and are known to be chemo- and radio-resistant. After surgical resection, the recurrence rate is high and overall survival limited. As current adjuvant treatments are ineffective, new treatment concepts are urgently needed. 5-aminolevulinic acid-based photodynamic therapy (5-ALA based PDT) showed promising results for malignant gliomas. However, it is unknown so far, whether chordomas accumulate protoporphyrin IX (PPIX) after application of 5-ALA and whether they are sensitive to subsequent 5-ALA based PDT.

METHODS

The immortalized human chordoma cells U-CH2 were used as in vitro model. After incubation for 4h or 6h with different 5-ALA concentrations, PPIX accumulation was determined by flow cytometry. To assess sensitivity to PDT, chordoma cells were incubated at 30.000cells/well (high cell density) or 15.000cells/well (low cell density) with graded doses of 5-ALA (0-50μg/ml) in 96-well plates and subsequently exposed to laser light of 635nm wavelength (18.75J/cm2). Cell survival was measured 24h after exposure to laser light using the WST-1 assay.

RESULTS

U-CH2 cells dose-dependently accumulated PPIX (ANOVA; p<0.0001). PPIX fluorescence was significantly higher, when cells were incubated with 5-ALA for 6h compared to 4h at higher 5-ALA concentrations (ANOVA/Bonferroni; p≤0.05 for≥30μg/ml 5-ALA). For both cell densities, a 5-ALA dose-dependent decline in viability was observed (ANOVA; p<0.0001). Viability was significantly lower at higher 5-ALA concentrations, when 30.000 cells/wells were treated compared to 15.000cells/well (ANOVA/Bonferroni; p≤0.001 for≥30μg/ml 5-ALA). LD50 was 30.25μg/ml 5-ALA.

CONCLUSION

The human UCH-2 cell line was a very useful in vitro model to study different effects of 5-ALA based PDT. For the first time, it could be shown that human chordoma cells may be destroyed by 5-ALA/PDT.