Does Low Level Laser Therapy (now Laser PBM) cause cancer?

By Jan Tunér

Even from the early years of LLLT it has been speculated about the possible cancerogenic risks of using this therapy. One thing can be safely stated: LLLT in itself never causes cancer, the wavelengths used are all out of the ionizing range of the electromagnetic spectrum. So far, so good. But the concern is rather the possible risk of irradiating known and especially unknown areas where malignant or pre-malignant cells are hidden. Here again we can safely say that the general rule is not to irradiate over known areas of malignancies. Not because LLLT necessarily would stimulate the malignant cells, but because we don’t know enough about this yet. Everyone agrees on this, so no cause for controversy. Then, we come to the core of the matter: what about irradiation over unknown areas where malignant or pre-malignant cells are hiding? The answer is that there is no 100% certainty in this area, at least not from a strict scientific angle. So let us see what research and experience there is.

First of all, let us look at the experience. LLLT has been used for some 60 years and still there is not a single report of any person having a hidden malignancy accelerated by LLLT. But on the other hand, if there had been such a case, would the connection be obvious and would it be reported? Thus, with hundreds of thousands of therapies, it would be unlikely not to have been discovered. And LLLT has indeed been extensively used for the treatment of the side effects of cancer treatment such as mucositis after radiation therapy and lymphedema after mastectomy [1,2]. These patients have been treated under the surveillance of oncologists and no negative effect have been reported. The concern is that even after radiation and mastectomy, some malignant cells would still be present and then stimulated by the LLLT. But no such reports found.

Indeed, one of the first report on the use of LLLT was published in 1964 by McGuff [3,4]. These researchers implanted tumour into the cheeks of hamsters and irradiated the animals with ruby or HeNe laser. To their surprise, many of the tumours disappeared and at any rate, the irradiated animals lived longer than those in the non-irradiated control group. The mechanism? More about that later.

Now, let us check some in vitro papers. What they report is that some tumor cells are stimulated by LLLT, other not. But a clear stimulation of some cells to be concerned. Still, these are in vitro studies and no immune system present. The in vivo situation is completely different, as we can see in the studies by McGuff. The comparisons between in vitro and in vivo are indeed scarce, but here is one by de Monteiro [5]:

Squamous cell carcinoma (SCC) is the most common neoplasm of the oral cavity. It is aggressive, highly proliferative, and metastatic. This stud] aimed to evaluate the effect of LLLT and imiquimod on DMBA chemically induced lesions on the oral mucosa of hamsters. SCCs were induced on 25 hamsters. Animals of G1 (control 1) were killed and the presence of tumors confirmed; G2 (control 2) suffered no interventions for additional 4 weeks; animals of G3 (laser treatment) were irradiated (λ660 nm, 50 mW, CW, Ø=3 mm, 0.07 cm2, 714.2 mW/cm2, 133 s, 95 J/cm2, 6.65 J) at every other day for 4 weeks; animals of G4 (imiquimod treatment) received 5 % imiquimod three times a week for 4 weeks; and animals of G5 (imiquimod and laser treatment) received both treatments for the same period. Samples were taken and underwent histological analysis by light microscopy and were investigated using immunohistochemistry for S-100(+) dendritic cells. In G1, G2, and G3, the evaluations showed malignant tumors and the absence of S-100(+) dendritic cells in the tumor stroma. In G4, 60 % of the animals had no malignant tumors, and S-100(+) dendritic cells were present in the stroma of the tumors as well as dysplasia. In G5, 40 % of the animals presented SCC, with scarce or no S-100(+) dendritic cells. The imiquimod treatment played a direct effect on SCC, demonstrated by the increased number of S-100(+) dendritic cells, which could suggest an important role of immune surveillance against neoplastic proliferation. Furthermore, its association with laser needs to be further investigated.

Here we can conclude that the LLLT had no positive effect, but on the other hand it had no negative effect either. So let us look at another study:

It has been speculated that the biostimulatory effect of Low Level Laser Therapy could cause undesirable enhancement of tumor growth in neoplastic diseases. The aim of the study by Frigo [6] was to analyze the behaviour of melanoma cells (B16F10) in vitro and the in vivo development of melanoma in mice after laser irradiation.

The authors performed a controlled in vitro study on B16F10 melanoma cells to investigate cell viability and cell cycle changes by the Tripan Blue, MTT and cell quest histogram tests at 24, 48 and 72 h post irradiation. The in vivo mouse model (n = 21) of melanoma was used to analyze tumor volume and histological characteristics. Laser irradiation was performed three times (once a day for three consecutive days) with a 660 nm 50 mW CW laser, beam spot size 2 mm2, irradiance 2.5 W/cm2 and irradiation times of 60s (dose 150 J/cm2) and 420s (dose 1050 J/cm2) respectively.

There were no statistically significant differences between the in vitro groups, except for an increase in the hypodiploid melanoma cells (8.48 +/- 1.40% and 4.26 +/- 0.60%) at 72 h post-irradiation. This cancer-protective effect was not reproduced in the in vivo experiment where outcome measures for the 150 J/cm2 dose group were not significantly different from controls. For the 1050 J/cm2 dose group, there were significant increases in tumor volume, blood vessels and cell abnormalities compared to the other groups.

LLLT Irradiation should be avoided over melanomas as the combination of high irradiance (2.5 W/cm2) and high dose (1050 J/cm2) significantly increases melanoma tumor growth in vivo.

In this study, LLLT obviously did have a negative effect. Or had it really? For the 150 J/cm2 there was no adverse effect. And 150 J/cm2 is pretty high. The negative effect appeared in the 1050 J/cm2. Is such a high intensity really “biostimulation”? And for a small mouse! Even 150 J/cm2 seems to be very intense for a mouse. Thus, I cannot conclude that this study supports any fear.

Gomes Henriques [7] used energies within the traditional therapeutic window and did find a stimulating effect on oral squamous cell carcinoma cells in vitro:

The proliferative potential was assessed by cell growth curves and cell cycle analysis, whereas the invasion of cells was evaluated using a Matrigel cell invasion assay. Expression of cyclin D1, E-cadherin, β-catenin, and MMP-9 was analysed by immunofluorescence and flow cytometry and associated with the biological activities studied. LLLT induced significantly the proliferation of SCC25 cells at 1.0 J/cm2, which was accomplished by an increase in the expression of cyclin D1 and nuclear β-catenin. At 1.0 J/cm2, LLLT significantly reduced E-cadherin and induced MMP-9 expression, promoting SCC25 invasion. The results of this study demonstrated that LLLT exerts a stimulatory effect on proliferation and invasion of SCC25 cells, which was associated with alterations on expression of proteins studied.

A stimulating effect was also found in the experiment by Sperandio [8], here is the summary:

This study demonstrated that LLLT (GaAlAs-660 nm or 780 nm, 40 mW, 2.05, 3.07 or 6.15 J/cm²) can modify oral dysplastic cells (DOK) and oral cancer cells (SCC9 and SCC25) growth by modulating the Akt/mTOR/CyclinD1 signalling pathway; LLLT significantly modified the expression of proteins related to progression and invasion in all the cell lines, and could aggravate oral cancer cellular behaviour, increasing the expression of pAkt, pS6 and Cyclin D1 proteins and producing an aggressive Hsp90 isoform. Apoptosis was detected for SCC25 and was related to pAkt levels.

Rather, the following recent study [9] gives a rather reassuring message:

The main aim of the study by Ottaviani [9] was to provide an answer to the safety of laser therapy when performed on neoplastic areas and its role on the immune system activation.

The authors created a mouse model of oral carcinogenesis: a chemical carcinogen (4-NQO) dissolved in the drinking water was administered to C57BL/6 female mice (n = 50), 8-week old, since this compound it induced the formation of multiple oral tumours. Among these, 25 mice under-went to 4 session of laser therapy (970 nm, 2.5 W/cm2, duty cycle 50%, 2 Hz, energy density 180 J/cm2) on consecutive days, while the remaining mice were used as controls. During the 21st week, animals were sacrificed to perform an accurate histological analysis of their tongue.

Moreover we established a tumour xenograft mouse model: melanoma cells were implanted in C57BL/6 female mice (n = 16), 6-week old, at the dorsal subcutaneous level. On day 10 tumour masses were visible to the naked eye, so mice were homogeneously divided into 4 groups according to tumour size: 3 groups were subjected to different laser protocols (660 nm,100 mW/cm2, continuous wave, 3 J/cm2; 800 nm, 1 W/cm2, continuous wave, 20 J/cm2 and 970 nm, 60 mW/cm2, continuous wave, 6 J/cm2) for 4 consecutive days (days 11 to 14), while the fourth group was used as control. On day 15, all animals were euthanized to measure tumour volume and weight. A deep histological analysis on tumour invasion and cancer immune response (CD1a, CD4, CD8, CD25, CD68 kp1 and Melan-A) was performed, as well as the analysis of the expression levels of cytokines involved in the immune system activation (TNF, IFN). Finally, we applied the same laser protocols on primary mouse bone marrow dendritic cells, with and without lipopolysaccharide stimulation.

A noteworthy decrease concerning the number/extension of dysplastic and neoplastic areas was registered in the laser treated group concerning the carcinogenesis mouse model (p<0.040). Moreover, treated animals showed a tendency to border and to isolate tumour areas. Laser therapy did not foster tumour growth or invasiveness (CD68 kp1 and Melan-A), but rather seemed to contain its extension. Moreover, in the laser groups, tumour infiltration by immune cells was much more higher compared to the control ones (CD4+, CD8+, CD25+ cells), consistent with the increased expression of IFN g (p<0.050). Of notice, CD1a positive dendritic cells were particularly abundant in the dermis in the control group, while they migrated to “wrap” the tumour in laser groups. Dendritic cells did not enhance their metabolism upon laser treatment, but reduced TNF and increased IFN.

From both in vitro and in vivo analysis we can state that the laser therapy is effective in boosting a potent immune response in vivo. According to these obtained results, we can therefore foresee that the treatment of cutaneous and mucosal lesions in oncological patients could be safely performed even in potentially dysplastic or neoplastic areas. Moreover, the direct effect of laser on immune system activation could open new interesting research fields.

What can we learn from the above? My conclusion is that malignant and pre-malignant cells indeed can be stimulated by LLLT. However, there is a simultaneous stimulation of the greatest healer of them all: our own immune system. And the immune system wins, if the irradiation is within traditional therapeutic windows.

Can we then rule out the possibility of this feared side effects of LLLT? No, it would be a premature conclusion, but based upon present Best Evidence – yes we can. And putting the unproven risk into proportion, just read the up-side/down-side list of serious side effects from popular pharmaceuticals! We need to balance between the pros and the (possible) contras and it seems this is not a big deal in pharmaceutical circles.

Finally, let us consider the fact that all medical lasers have biostimulatory effects. Millions of persons have been subjected to laser treatment for tattoo removal, skin resurfacing, liposuction etc., and there are no reports of stimulation of latent cancer cells, nor any considerations about looking for hidden malignant cells before performing these treatments. And indeed, even when using surgical lasers in cancer areas, the concern about a simultaneous stimulation of the cancer cells seems to be absent.

[1] Dirican A, Andacoglu O, Johnson R, McGuire K, Mager L, Soran A. The short-term effects of low-level laser therapy in the management of breast-cancer-related lymphedema.Support Care Cancer. 2011; 19 (5): 685-690.

[2] Mourão e Lima M T, E Lima J G, de Andrade M F, Bergmann A. Low-level laser therapy in secondary lymphedema after breast cancer: systematic review. Lasers Med Sci. 2012 [Epub ahead of print]

[3] McGuff P E. Tumoricidal effect of laser radiation on malignant tumors. Int Ophthalmol Clin. 1966; 6 (2): 379-386.

[4] McGuff P E, Gottlieb L S, Katayama I, Levy C K. Comparative study of effects of laser and/or ionizing radiation therapy on experimental or human malignant tumors. Am J Roentgenol Radium Ther Nucl Med. 1966; 96 (3): 744-748.

[5] de C Monteiro J S, de Oliveira SC, Reis Júnior J A, Gurgel C A, de Souza S C, Pinheiro A L, dos Santos J N. Effects of imiquimod and low-intensity laser (λ660 nm) in chemically induced oral carcinomas in hamster buccal pouch mucosa. Lasers Med Sci. 2013;28(3):1017-1024.

[6] Frigo L, Luppi J S, Favero G M, Maria D A, Penna S C, Bjordal J M, Bensadoun R J, Lopes-Martins R A. The effect of low-level laser irradiation (In-Ga-Al-AsP - 660 nm) on melanoma in vitro and in vivo. BMC Cancer. 2009; 20; 9: 404.

[7] Gomes Henriques A C, Ginani F, Oliveira R M, Keesen T S, Galvão Barboza C A, Oliveira Rocha H A, de Castro J F, Della Coletta R, de Almeida Freitas R. Low-level laser therapy promotes proliferation and invasion of oral squamous cell carcinoma cells. Lasers Med Sci. 2014 [Epub ahead of print]

[8] Sperandio F F, Giudice F S, Corrêa L, Pinto D S Jr, Hamblin M R, de Sousa S C. Low level laser therapy can produce increased aggressiveness of dysplastic and oral cancer cell lines by modulation of Akt/mTOR signaling pathway. J Biophotonics. 2013 [Epub ahead of print]

[9] Ottaviani G, Zacchigna S, Gobbo M, Rupel K, Di Lenarda R, Biasotto M. Laser effect on immune system activation. Laser Therapy. 2015; 24 (2): 125. Abstracts from IPTA 6th Congress, Nice, France, 2015.