Category: Cancer

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Selenium and Drug-Resistant Breast Cancer

What continues to be a problem in breast cancer therapy?

Over time, many breast tumors become resistant to chemotherapy. Thus, drug-resistant tumors limit the success of anti-cancer therapies. Numerous mechanisms decrease the intracellular accumulation of anti-cancer drugs. In this way, breast cancer tumors become less responsive to the chemotherapy [Bajer 2026].

Does supplementary selenium have anti-cancer properties?
Breast cancer survivors
In breast cancer treatment, selenium compounds may help to reverse resistance to chemotherapy. The selenium may help to sensitize aggressive breast cancer cells to standard chemotherapies. We need clinical trials to establish selenium form and dosage.

Selenium is an essential trace element. Through the activity of selenoproteins, selenium is involved in the following potentially anti-cancer activities [Bajer 2026]:

  • Antioxidant defense
  • Immune modulation
  • Redox regulation

Note: Cancer cells often rely on altered redox balance. Accordingly, selenium compounds may disrupt tumor survival mechanisms. At the same time, they can spare normal cells and tissues.

How do selenium compounds attack drug-resistant cancer?

In a 2026 review, Bajer et al make the point that multi-drug resistance in breast cancer often stems from several resistance pathways acting together. Thus, selenium-containing compounds may help overcome breast cancer patients’ multi-drug resistance via overlapping multiple mechanisms: read more

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Selenium for Adjuvant Cancer Treatment

Cancer treatment. What do we know at the present time about the effectiveness of selenium as an adjuvant treatment in cancer patients?
In a 2024 systematic review, researchers have evaluated the existing evidence from data from 12 studies with 2,483 adult patients undergoing cancer treatment. The types of cancer included non-Hodgkin lymphoma, head and neck cancer, thyroid cancer, acute myeloid or acute lymphocytic leukemia, stage I non-small lung cancer, breast cancer, cervical and endometrial cancer, prostate cancer, and non-invasive urothelial carcinoma [Krannich 2024].

Cancer patient
More information is needed about the effects of adjuvant treatment of cancer patients with selenium supplements. Similarly, more information is needed about the concurrent use of selenium supplements in patients receiving chemotherapy and radiation therapy.

The researchers’ analysis of the available data does not give a clear picture of the efficacy of selenium administration to adult cancer patients. One reason is that several of the evaluated studies did not report measurements of the patients’ serum selenium levels at the beginning or the end of the study. The studies that did report serum selenium levels used different ways to measure selenium levels. Moreover, the duration of the selenium administration and the type of selenium preparation and the dosage varied from study to study [Krannich 2024]. read more

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Selenoprotein P Status and Colorectal Cancer Mortality

Selenium deficiency, especially as manifested in low circulating levels of selenoprotein P, is associated significantly with an increased risk of colorectal cancer incidence and mortality [Pal 2024; Brezina 2025]. SELENOP is a selenium-dependent glycoprotein that is the primary transporter of selenium to the tissues and organs. SELENOP also acts to reduce oxidative stress and systemic inflammation [Schöttker 2024; Brezina 2025].

Newspaper article about cancer
Colorectal cancer risk is elevated in selenium and SELENOP deficiency. Serum SELENOP concentration is perhaps the single most useful parameter for prognosis once the diagnosis has been made. SELENOP concentrations below 2.5 mg/L indicate severe deficiency. Concentrations below 5.0 mg/L suggest elevated risk.

In the Colorectal Cancer Study of Austria (CORSA Study), researchers analyzed data from 519 participants (n = 153 tumor-free controls, n = 255 patients with adenomas, and n = 111 patients with colorectal cancer). The median age of the study participants was 65 years. Nearly two-thirds of the study participants were male. The study participants’ median plasma selenium concentration was a very low 65.7 mcg/L. Their median SELENOP concentration was also low:  2.7 mg/L. During a median follow-up period of 5,424 days (almost 15 years), there were 210 deaths (40 %) [Brezina 2025]. read more

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Selenium and Cancer Treatment

Adult cancer patients who have a selenium deficiency can benefit from selenium supplementation during their radiotherapy and/or chemotherapy. This is the conclusion from a 2024 systematic review. The researchers examined the pooled data from 12 clinical studies enrolling 2,483 patients. The reviewed studies investigated the use of selenium substitution therapy in adult cancer patients undergoing cancer treatment [Krannich 2024].

Doctor advising cancer patient
A review of 15 years of selenium supplementation has shown promising results in radiation therapy in tumor patients with a relative selenium deficit.

The researchers defined selenium deficiency as serum or plasma selenium concentrations below 80 mcg/L or as whole blood selenium concentrations below 100 mcg/L. Furthermore, they regarded serum or plasma selenium levels over 130 mcg/L as replete status [Krannich 2024]. read more

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Selenium and Cancer Prevention – the Evidence

The evidence for the use of selenium supplementation in cancer prevention is still inconclusive. Rataan et al suggest that the fault may lie in the design of the existing studies. At least two factors have contributed to this lack of conclusive evidence:

  • the use of different compounds in the tests of selenium and cancer
  • the different blood selenium levels of the study participants at baseline
Cancer patients
Selenium supplementation of individuals with low dietary intakes of selenium may help prevent the development of certain types of cancer.

As an example, Rataan et al cite the differences between the Nutritional Prevention of Cancer (NPC) trial and the Selenium and Vitamin E Cancer Prevention Trial (SELECT). In the NPC study, the researchers used a selenium-enriched yeast supplement. This yeast formulation contained mostly selenomethionine but also contained several other selenium species including Se-methylselenocysteine. In the SELECT study, the researchers used a 100% selenomethionine supplement. It now seems clear that the chemopreventive effect of selenium that was seen in the NPC study but not seen in the SELECT study must have come from some selenium species other than selenomethionine. The most likely chemopreventive selenium species is the Se-methylselenocysteine [Rataan 2022; Marshall 2017]. read more

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Selenium May Reduce the Risk of Heart Disease and Some Cancers

Reduced risk of heart disease and reduced risk of some cancers. Increasing the daily intake of selenium among individuals with low selenium status may reduce the risk of cardiovascular disease and some cancers. The available data seem to show that most adults in the Nordic and Baltic countries, with the exception of adults in Finland, have low selenium intakes and low selenium status [Alexander & Olsen 2023].

Jan Alexander
Prof. Jan Alexander, MD, PhD, Norwegian Institute of Public Health in Oslo, says: There are various factors that influence cardiovascular disease mortality and cancer incidence: diet, lifestyle, genetics, inter alia. The impact of these factors varies from one Nordic country to the next.

Selenium is an essential trace element. The human body cannot synthesize it. It must come from the diet and supplements. Selenium is a vital component of selenoproteins that are critical to normal health and physiological functioning. This is the fundamental message from a 2023 selenium scoping review conducted for the Nordic Nutritional Recommendations 2023 [Alexander & Olsen 2023]. read more

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Selenium and Radiation Therapy for Cancer Patients

Cancer patients tend to have reduced serum selenium concentrations compared to healthy controls. Adjuvant selenium supplementation improves the protection of healthy tissue in tumor patients undergoing radiation therapy [Muecke 2018].

Cologne cathedral in Germany
15 years of experience with adjuvant selenium supplementation in radiation oncology in Germany has yielded a solid knowledge database. As a result,  some radiation oncologists measure the patient’s selenium levels during therapy and compensate in cases of selenium deficiency. Even so, it is important to remember that selenium status is  a relatively small piece in the bigger puzzle of therapeutic success in radiation oncology.

In a 2018 review of 15-years of experience with selenium supplementation in radiation oncology, Muecke et al [2018] reported on two randomized controlled trials. The researchers observed positive effects of the supplemental selenium and no adverse effects in the patients undergoing radiation therapy:

  • 81 patients with uterine cancer
  • 39 patients with head and neck tumors
Selenium Deficit in Cancer Patients

In the majority of the tumor patients (carcinomas of the uterus, head and neck, lungs, rectum or prostate) whom they examined, German researchers found a relative selenium deficit in whole blood or serum [Muecke 2018]. read more

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Selenium Supplementation and Chemotherapy in Cervical Cancer Patients

Selenium yeast supplementation administered concurrently with chemotherapy and radiation therapy effectively increased blood selenium levels in cervical cancer patients with inadequate selenium status. The selenium yeast supplementation was used as an adjuvant treatment to the standard chemotherapy and radiation therapy. It significantly decreased the hematologic toxicity of the chemoradiotherapy [Yang 2023].

Cancer and selenium
Each year, worldwide, half a million women are diagnosed with cervical cancer, and 300 000 die from the disease. In most cases, the human papilloma virus is the cause of the disease [Cohen 2019]. The trace element selenium has antiviral properties. Cell studies and mouse studies of cervical cancer have shown that different selenium species have anticancer effects in cervical cancer induced by human papilloma virus or by chemical carcinogens [Jablonska 2021].
In a randomized controlled trial, researchers randomly assigned 104 patients diagnosed with stage IIB cervical cancer receive 100 mcg selenium yeast tablets (n=50) or matching placebos twice daily (n=54) for five weeks [Yang 2023].

All patients in both groups received the standard treatment including pelvic external irradiation, concurrent five cycles of chemotherapy, and brachytherapy [Yang 2023]. read more

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Breast Cancer Recurrence and Selenoprotein P Autoimmunity

Breast cancer prognosis is especially poor in patients with low serum selenium and serum selenoprotein P concentrations. Now, researchers have discovered natural autoantibodies with antagonistic properties to selenoprotein P uptake in breast cancer patients and  in patients with thyroid disease [Demircan 2022; Sun 2022].

Autoimmunity
Autoimmunity is the production of antibodies against the tissues or substances of one’s own body, resulting in an autoimmune disease or hypersensitivity reaction. Autoantibodies to Selenoprotein P impair the transport of the essential trace element selenium in breast cancer patients and in Hashimoto’s thyroiditis patients.

Selenium is an essential trace element that has numerous biological functions in the body, most of which are carried out by selenium-containing selenoproteins. Among the more important selenoproteins are selenoprotein P, the main transporter of selenium in the blood, and glutathione peroxidase 3 (GPX3), an important antioxidant.

The human body does not synthesize selenium. Human cells are dependent upon selenium sources in the diet. Unfortunately, the selenium content in the soil and in food varies considerably from region to region in the world. For example, the plasma selenium concentrations in people living in much of Europe are generally below, often well below, 80–90 mcg/L whereas people living in North America generally have plasma selenium levels above 120 mcg/L [Alehagen 2022]. read more

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Selenium Exposure Studies

Selenium exposure in the diet and in supplements: in this review article, we summarize the key outcomes of the best selenium exposure studies.

Optimal Selenium Intake and Status

In his review of the available research literature, Professor Urban Alehagen, Linköping University, Sweden, concluded that a daily intake of 100–150 mcg of selenium per day is required.

This is the intake level that enables an optimal expression of the important selenoprotein P that transports selenium from the liver to peripheral tissues [Alehagen 2022].  For other selenoproteins to be optimized, i.e., to be fully expressed, Prof. Alehagen argues that selenium status of approximately 120 mcg/L when measured in red blood cells is necessary [Alehagen 2022]. read more