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This capacity could be an interesting way of overcoming the problem of death resistance displayed by many
tumors since one of the characteristics that is important for an alternative therapy for cancer treatment is to
broaden the spectrum of cell death mechanisms being gathered in order to by-pass the different resistance
mechanisms displayed by malignant cells.

Finally, even if more research is still needed in the field including the development and optimization of PS
synthesis in order to increase the efficiency on specific tumor cell damage, light sources and irradiation
protocols, it is evident that in the majority of the cases, PDT represents a suitable therapeutic alternative
presenting several advantages over the traditional clinical approaches for cancer treatments. It is clear that
PDT deserves more opportunities and investment in clinical trials. By doing so, it could be expected that the
increase in the number of clinical studies with metastatic or non-mestastatic cancer, in the near future, could
allow the scientific and clinical community to make more robust conclusions about PDT’s real translational
potential to become a standard first-line therapy, either alone or in combination with other treatments, for a
wide variety of tumors.

DECLARATIONS
Authors’ contributions
Responsible for the paper: Baptista MS, Labriola L
Concept, design, definition of intellectual content: dos Santos AF, Baptista MS, Labriola L
Literature search, manuscript preparation and revision: dos Santos AF, de Almeida DRQ, Terra LF, Baptista
MS, Labriola L
Manuscript editing: dos Santos AF, Labriola L

Availability of data and materials
Not applicable.

Financial support and sponsorship
This work was supported by CAPES, CNPq and FAPESP (2017/03618-6; 2016/04676-7 and 2013/07937-8).

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Copyright
© The Author(s) 2019.

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