Chemobrain and Brain Fog
Guideline: NCCN Survivorship Guidelines 2025; ACS chemobrain guidance
Medically reviewed by Dr. Alexandru-Theodor Amarfei, M.D.
First published
Quick Answer
Chemobrain can contribute to brain fog. The most useful clues are the symptom pattern, nearby overlaps, and whether the mechanism described here matches your story: Cancer-related cognitive impairment (chemobrain or chemofog) affects 15-75% of cancer patients and can persist for months to years after treatment ends.
When to expect improvement
Immediate (screening); rehab timeline 3-12 months
If no improvement after this timeframe, it's worth exploring other possibilities.
Is Chemobrain Brain Fog Reversible?
Chemobrain often improves over time, though recovery is variable. Most people see improvement within months to a year, though some have persistent effects. Exercise, cognitive rehab, and addressing co-factors (sleep, anemia, hormones) can accelerate recovery.
Cause Visual
Chemobrain Pattern Map
Pattern-focused visual for Chemobrain with mechanism, timing, action, and clinician discussion cues.
The Science Behind Chemobrain Brain Fog
Chemobrain usually feels like a real drop from baseline after treatment: slower recall, reduced mental stamina, harder word-finding, and a lower tolerance for multitasking.
What this pattern often feels like
These community-grounded clues are here to help you recognize the shape of the pattern. They are not a diagnosis.
Chemobrain usually presents as a clear post-treatment decline in cognitive stamina, word finding, and working memory rather than a lifelong or purely situational pattern.
Differentiator question: Did the fog become substantially worse during or after cancer treatment, with reduced mental stamina and worse recall than your old baseline?
Treatment effects may be central, but anemia, sleep disruption, menopause, mood, and pain often add to the same cognitive burden.
Chemobrain Brain Fog Symptoms: How It Usually Shows Up
These are pattern signals, not proof by themselves. Use them to guide what to measure, compare, and discuss next.
Chemobrain can present with morning-heavy fog when sleep or overnight physiology is relevant.
Post-meal worsening can strengthen Chemobrain when metabolic or inflammatory triggers are involved.
Post-exertional worsening can increase confidence for Chemobrain when recovery capacity is reduced.
What to Try This Week for Chemobrain
- 4
Drink a glass of water now. Keep a bottle visible. Aim for pale yellow urine. Don't overthink it - just drink regularly.
Weekly focus: Hydration.
- 5
Open a window for 15 minutes. Fresh air exchange reduces indoor pollutants. If outdoors is bad (pollution, pollen), use a HEPA filter.
Weekly focus: Environment.
- 6
Reach out to one person today. Text, call, walk together. Isolation worsens every cause of brain fog. Connection is a biological need, not a luxury.
Weekly focus: Connection.
- 7
Rate your brain fog 1-10 each morning for 7 days. Note sleep quality, food, exercise, stress. Patterns emerge within a week.
Weekly focus: Tracking.
Is Chemobrain Brain Fog Reversible?
Chemobrain often improves over time, though recovery is variable. Most people see improvement within months to a year, though some have persistent effects. Exercise, cognitive rehab, and addressing co-factors (sleep, anemia, hormones) can accelerate recovery.
Typical timeline: Many improve within 6-12 months post-treatment. Some experience effects for years. Exercise-based interventions can show benefits within weeks to months.
Factors that affect recovery:
- Type of chemotherapy (some agents more neurotoxic)
- Total treatment burden (chemo + radiation + surgery + hormonal therapy)
- Age at treatment
- Pre-treatment cognitive reserve
- Co-factors: anemia, sleep, depression, hormonal changes
- Access to cognitive rehabilitation
Source: Campbell et al., J Clin Oncol, 2019; NCCN Survivorship Guidelines
Food Approach
Primary Option
Gentle Anti-Inflammatory (Recovery-Adapted)
For people who are too fatigued, nauseous, or overwhelmed for complex dietary changes. The minimum effective dose.
Small, frequent, simple meals. Broth/soup if appetite is poor. Add ONE portion of oily fish per week. Add berries when tolerable. Reduce (don't eliminate) ultra-processed food. Hydrate. Don't force large meals.
Eat enough - treatment often suppresses appetite. Mediterranean pattern when tolerable. Small frequent meals if nauseous. Protein for tissue repair. Don't force 'clean eating' during chemo - calories and protein matter more than perfection. If appetite is zero, nutrition shakes count.
Open primary diet pattern →Alternative Options
Iron-Repletion Focus
For confirmed or suspected iron deficiency. Pair iron-rich foods with vitamin C. Separate from tea/coffee/dairy.
Iron-rich foods: red meat 2-3x/week, liver 1x/week (if tolerated), lentils, spinach, fortified cereals. ALWAYS pair with vitamin C (bell pepper, orange, kiwi, strawberry). Avoid tea/coffee within 1hr of iron-rich meals. Continue prenatal vitamins if postpartum.
Open this option →Low-FODMAP (Phased — Monash Protocol)
Evidence-based for IBS/SIBO. Three phases: elimination, reintroduction, personalization.
Phase 1 (2-6 weeks): Remove high-FODMAP foods (onion, garlic, wheat, beans, certain fruits). Phase 2: Reintroduce one group at a time. Phase 3: Personalized diet keeping only YOUR trigger foods out. Use the Monash FODMAP app for portions.
Open this option →How to Talk to Your Doctor About Chemobrain and Brain Fog
Suggested Script
"I want to evaluate whether my cognitive symptoms fit treatment-related chemobrain and what overlapping factors like sleep, anemia, pain, or medication effects still need to be ruled out."
Tests To Discuss
- • Medication Review
- • Neuropsychological Testing
- • CBC + CMP
Differentiator Questions
- • Did the brain fog clearly change during or after chemotherapy, endocrine therapy, or cancer-related treatment?
- • What part of this looks treatment-related versus sleep apnea, anxiety, or anemia overlap?
- • Is the main problem processing speed and mental stamina rather than a trigger-linked crash pattern?
Quiet next step
Get the doctor handout for this pattern
Get the printable doctor handout for this pattern and keep the next steps in one place. No funnel, just the handout and a quiet email reminder if you want it.
How Chemobrain Brain Fog Connects Across The Site
Protocol Guides
Clarity Code Factors
- Depletion
Nutrient, oxygen, or energy substrate deficits reduce cognitive reserve and day-to-day reliability.
- Dysregulation
Circadian, autonomic, or stress-regulation instability often drives fluctuating fog patterns.
Quick Summary: Chemobrain Brain Fog Key Points
Informative- 1
Chemobrain usually feels like a real drop from baseline after treatment: slower recall, reduced mental stamina, harder word-finding, and a lower tolerance for multitasking.
- 2
Worse in the morning: Symptoms often worsen with cumulative fatigue, poor sleep, treatment cycles, pain flares, or overloading the brain with multitasking.
- 3
After-meal worsening: Many people describe a lower ceiling for cognitive stamina rather than a single predictable trigger window.
- 4
Worse after exertion: A treatment-related onset or worsening is more informative than the exact severity score.
- 5
Story language directly matches a recurring Chemobrain pattern rather than broad fatigue alone.
- 6
Symptoms recur with a repeatable trigger/timing pattern that is physiologically plausible for Chemobrain.
- 7
Context clues (history, exposures, or coexisting conditions) support Chemobrain as a priority hypothesis.
- 8
At least two independent signals point in the same direction without strong contradiction.
- 9
Response to relevant interventions tracks closer with Chemobrain than with Pain.
- 10
A competing cause (Pain) has stronger direct evidence in the story.
Metabolic Lens
Secondary overlapThis cause can overlap with metabolic-pattern brain fog. Distinguish by timing, trigger profile, and objective context before narrowing to one explanation.
- Fog episodes that cluster in repeatable timing windows (meal, exertion, posture, or sleep-pattern linked).
- Energy or clarity drops that feel abrupt rather than uniformly low all day.
- Symptom overlap with sleep, autonomic, anxiety, or medication factors.
These pattern clues can raise suspicion but are not diagnostic on their own; confirmation requires clinician-guided evaluation and objective data.
11 Evidence-Based Insights About Chemobrain and Brain Fog
You survived cancer. Now you can't think. You're told 'at least you're alive' when you report that you can't remember what you just read. Chemobrain is real, it's measurable, and there ARE things that help. You don't have to accept it as the price of survival.
Evidence grades: A = strong human evidence, B = moderate evidence, C = preliminary or small-study evidence. Full grading guide
1 THE SYMPTOM INVENTORY: Rate these 1-10 right now: Difficulty concentrating.
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THE SYMPTOM INVENTORY: Rate these 1-10 right now: Difficulty concentrating.
Trouble finding words. Memory problems. Slower thinking. Trouble multitasking. If you're scoring 6+ on multiple, you have cancer-related cognitive impairment. It has a name. It's real.
FACT-Cog; NCCN Survivorship Guidelines
2 15-75% of cancer patients experience cognitive changes.
▼
15-75% of cancer patients experience cognitive changes.
It's not just chemotherapy - surgery, radiation, immunotherapy, hormonal therapy, steroids, and the cancer itself all contribute. If you had cancer treatment, cognitive changes are common, not rare.
NCCN Survivorship Guidelines 2025
3 THE MEDICATION AUDIT: List every medication you're currently taking.
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THE MEDICATION AUDIT: List every medication you're currently taking.
Are you on: tamoxifen? Aromatase inhibitor? Pain medications? Anti-nausea drugs? Steroids? Sleep aids? Calculate your Anticholinergic Burden score (ACB calculator online). High ACB = worse cognition.
NCCN; American Cancer Society
4 Exercise is the most evidence-based treatment for chemobrain.
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Exercise is the most evidence-based treatment for chemobrain.
A 2025 meta-analysis confirms: aerobic exercise improves cognitive function during AND after cancer treatment. Start with 10 minutes. The evidence is stronger for exercise than for any supplement.
Campbell et al., J Clin Oncol 2019
5 THE 10-MINUTE WALK TEST: Can you do a 10-minute walk today?
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THE 10-MINUTE WALK TEST: Can you do a 10-minute walk today?
Even during active treatment? Even on chemo days? Light walking is safe for most cancer patients and proven to help cognition. Start there. Build slowly.
NCCN exercise guidelines; Schmitz et al., CA Cancer J Clin 2019
6 THE EXTERNAL MEMORY SYSTEM: Your brain works differently now.
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THE EXTERNAL MEMORY SYSTEM: Your brain works differently now.
Work WITH it, not against it. Today: set 3 phone reminders. Write tomorrow's to-do list before bed. Put keys in the same place every time. External systems replace what internal memory lost.
Cognitive rehabilitation approach
7 Tell your oncology team.
▼
Tell your oncology team.
Most cancer centers now have survivorship programs with cognitive rehabilitation, neuropsychology, and occupational therapy. You don't have to 'just live with it.' These services exist. Ask for them.
NCCN Survivorship Guidelines
8 Recovery timeline: 6-12 months for many people.
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Recovery timeline: 6-12 months for many people.
Some experience symptoms for years, but most improve significantly after treatment ends. Track your symptoms monthly. The trajectory matters. Most people get better.
Longitudinal studies; NCCN
9 THE PACING EXERCISE: Rate your cognitive energy 1-10 in the morning, at noon, and at 4pm for 3 days.
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THE PACING EXERCISE: Rate your cognitive energy 1-10 in the morning, at noon, and at 4pm for 3 days.
When are you sharpest? Schedule demanding cognitive tasks for your peak. Accept that capacity varies. Pacing prevents crashes.
Occupational therapy; pacing guidance
10 'At least you're alive' is not a valid response to cognitive impairment.
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'At least you're alive' is not a valid response to cognitive impairment.
Quality of life matters. Cognitive function matters. Your concerns are legitimate medical issues that deserve attention, not dismissal.
Patient advocacy; NCCN
11 There IS hope.
▼
There IS hope.
With exercise, cognitive rehabilitation, medication optimization, and time, most people improve. You're not stuck. You're recovering. And now there are evidence-based interventions to help.
NCCN Survivorship Guidelines 2025
View all 11 citations ▼
- FACT-Cog; NCCN Survivorship Guidelines
- NCCN Survivorship Guidelines 2025
- NCCN; American Cancer Society
- Campbell et al., J Clin Oncol 2019
- NCCN exercise guidelines; Schmitz et al., CA Cancer J Clin 2019
- Cognitive rehabilitation approach
- NCCN Survivorship Guidelines
- Longitudinal studies; NCCN
- Occupational therapy; pacing guidance
- Patient advocacy; NCCN
- NCCN Survivorship Guidelines 2025
Common Questions About Chemobrain Brain Fog
Based on clinical evidence and community insights. Use these as discussion prompts with your doctor, not self-diagnosis.
1. Can chemobrain cause brain fog? ▼
Chemobrain can contribute to brain fog. The most useful clues are the symptom pattern, nearby overlaps, and whether the mechanism described here matches your story: Cancer-related cognitive impairment (chemobrain or chemofog) affects 15-75% of cancer patients and can persist for months to years after treatment ends.
2. What does chemobrain brain fog usually feel like? ▼
Cancer-related cognitive impairment (chemobrain or chemofog) affects 15-75% of cancer patients and can persist for months to years after treatment ends.
3. What should I try first if I think chemobrain is involved? ▼
Use single-tasking for one week instead of trying to multitask through the fog. Chemobrain often shows up as reduced cognitive bandwidth, not lack of effort. Start with one high-yield change before adding complexity.
4. What tests should I discuss for chemobrain brain fog? ▼
The most useful next tests depend on the pattern, but common discussion points include Medication Review, Neuropsychological Testing, CBC + CMP. Use the timing of your fog and the closest competing causes to narrow the first step.
5. When should I bring chemobrain brain fog to a clinician? ▼
STOP - Seek urgent oncology evaluation if: sudden severe headache, new seizures, vision changes, weakness on one side, or rapidly progressive confusion. These may indicate brain metastasis, stroke, or treatment-related toxicity, NOT typical chemobrain.
6. How is chemobrain brain fog different from sleep? ▼
What part of this looks treatment-related versus sleep apnea, anxiety, or anemia overlap?
7. Could this be Pain instead of Chemobrain? ▼
Pain-related fog usually rises with flares, poor sleep, or constant body load, while chemobrain is more tightly linked to treatment history, slowed processing, and persistent word-finding problems even when pain is quieter.
8. How quickly can I tell whether this path is helping? ▼
Improvement timing depends on the root driver. Track the pattern for 1 to 2 weeks before deciding whether this path is helping, unless the story includes urgent escalation features.
9. When should I take this to a clinician instead of self-tracking? ▼
Escalate when fog stays stable or worse after a focused 1-2 week trial, function keeps dropping, or your story includes red-flag features. Bring your trigger/timing log, medication list, and prior test results to save appointment time.
10. What do people usually try first when they suspect Chemobrain? ▼
A common first step from related community patterns is: Complete the FACT-Cog (Functional Assessment of Cancer Therapy - Cognitive Function) questionnaire. Track cognitive symptoms on a daily scale of 1-10. Share with your oncology team - most cancer centers now have survivorship programs that address cognitive symptoms with structured rehabilitation.
Source: Community pattern analysis (49 analyzed stories)
📖 Glossary of Terms (4 terms) ▼
Chemobrain
Chemobrain can contribute to brain fog.
blood-brain barrier
A selective membrane that controls what enters the brain from the bloodstream.
BDNF
Brain-derived neurotrophic factor — a protein that promotes neuron growth, survival, and new connections.
CBC
Complete blood count — a basic blood panel that measures red cells, white cells, and platelets.
Related Articles
Chemobrain and Brain Fog
Deep guide that expands the cause page with symptom-feel, differentiation, test triage, and doctor-prep language.
Sleep and Brain Fog
Nearby confusion-pair article for side-by-side differentiation.
Pain and Brain Fog
Nearby confusion-pair article for side-by-side differentiation.
When to Seek Urgent Help
STOP - Seek urgent oncology evaluation if: sudden severe headache, new seizures, vision changes, weakness on one side, or rapidly progressive confusion. These may indicate brain metastasis, stroke, or treatment-related toxicity, NOT typical chemobrain.
Deep Dive
Clinical Fit + Advanced Detail
▼
Deep Dive
Clinical Fit + Advanced Detail
How This Cause Is Evaluated
The analyzer ranks all 66 causes, but this page shows the exact clues that strengthen or weaken Chemobrain so your next steps stay logical.
Direct Evidence Needed
- ✓ Story language directly matches a recurring Chemobrain pattern rather than broad fatigue alone.
- ✓ Symptoms recur with a repeatable trigger/timing pattern that is physiologically plausible for Chemobrain.
Supporting Clues
- + Context clues (history, exposures, or coexisting conditions) support Chemobrain as a priority hypothesis. (weight 7/10)
- + At least two independent signals point in the same direction without strong contradiction. (weight 6/10)
- + Response to relevant interventions tracks closer with Chemobrain than with Pain. (weight 5/10)
What Lowers Confidence
- − A competing cause (Pain) has stronger direct evidence in the story.
- − Core expected signals for Chemobrain are missing across history, timing, and triggers.
Timing Patterns That Strengthen This Fit
Worse in the morning
Symptoms often worsen with cumulative fatigue, poor sleep, treatment cycles, pain flares, or overloading the brain with multitasking.
After-meal worsening
Many people describe a lower ceiling for cognitive stamina rather than a single predictable trigger window.
Worse after exertion
A treatment-related onset or worsening is more informative than the exact severity score.
Differentiate From Similar Causes
Question to ask
Does your pattern fit Chemobrain more consistently than Pain when timing, triggers, and recovery are compared side-by-side?
▼
Question to ask
Does your pattern fit Chemobrain more consistently than Pain when timing, triggers, and recovery are compared side-by-side?
If yes: Pattern consistency is stronger for Chemobrain.
If no: Pattern consistency is stronger for Pain.
Compare with Pain → Question to ask
Does your pattern fit Chemobrain more consistently than Sleep Apnea when timing, triggers, and recovery are compared side-by-side?
▼
Question to ask
Does your pattern fit Chemobrain more consistently than Sleep Apnea when timing, triggers, and recovery are compared side-by-side?
If yes: Pattern consistency is stronger for Chemobrain.
If no: Pattern consistency is stronger for Sleep Apnea.
Compare with Sleep Apnea → Question to ask
Does your pattern fit Chemobrain more consistently than Anxiety when timing, triggers, and recovery are compared side-by-side?
▼
Question to ask
Does your pattern fit Chemobrain more consistently than Anxiety when timing, triggers, and recovery are compared side-by-side?
If yes: Pattern consistency is stronger for Chemobrain.
If no: Pattern consistency is stronger for Anxiety.
Compare with Anxiety →How People Describe This Pattern
- • My most prominent issues are memory issues after chemo and word finding difficulty.
- • I also struggle significantly with slow processing after treatment.
- • These symptoms feel like a repeatable pattern that affects my cognition.
Often Confused With
Pain
OpenChemobrain and Pain can both present as fatigue + concentration problems when story detail is sparse.
Key question: When timing and trigger details are compared directly, which pattern fits better: Chemobrain or Pain?
Sleep Apnea
OpenChemobrain and Sleep Apnea can both present as fatigue + concentration problems when story detail is sparse.
Key question: When timing and trigger details are compared directly, which pattern fits better: Chemobrain or Sleep Apnea?
Anxiety
OpenChemobrain and Anxiety can both present as fatigue + concentration problems when story detail is sparse.
Key question: When timing and trigger details are compared directly, which pattern fits better: Chemobrain or Anxiety?
Use This Page With the Story Analyzer
Use this starter to run a focused check while still comparing all 66 causes:
"I want to check whether Chemobrain could explain my brain fog. My most relevant symptoms are memory issues after chemo, word finding difficulty, and it gets worse with active chemotherapy, sleep disruption."
Map My Pattern for ChemobrainBiomarkers and Tests
Neuropsychological Testing
Formal cognitive testing through neuropsychology. Establishes baseline, identifies specific deficits (memory, processing speed, executive function), guides targeted rehabilitation.
Evidence: Strong - recommended by NCCN for persistent post-treatment cognitive symptoms.
Source: NCCN Survivorship Guidelines 2025
Medication Review
Review ALL current medications with oncologist and pharmacist: hormonal therapy (tamoxifen, aromatase inhibitors), pain medications, anti-nausea drugs, steroids, sleep aids. Calculate Anticholinergic Burden (ACB) score.
Evidence: Strong - medication contribution is often underrecognized. Simple switches can significantly improve cognition.
Source: NCCN; American Cancer Society chemobrain guidance
Doctor Conversation Script
Bring concise evidence, request specific tests, and agree on rule-out criteria.
Initial Visit
"I want to systematically evaluate whether Chemobrain is contributing to my brain fog and compare it against close alternatives."
Key points to emphasize
- • Please document what findings would confirm this cause versus lower confidence.
- • I want an evidence-first workup with clear follow-up criteria.
- • Please note which competing causes should be checked in parallel if results are inconclusive.
- • Please separate metabolic, sleep, autonomic, and medication overlap before narrowing to one cause.
Tests to discuss
Neuropsychological Testing
Formal cognitive testing through neuropsychology. Establishes baseline, identifies specific deficits (memory, processing speed, executive function), guides targeted rehabilitation.
Medication Review
Review ALL current medications with oncologist and pharmacist: hormonal therapy (tamoxifen, aromatase inhibitors), pain medications, anti-nausea drugs, steroids, sleep aids. Calculate Anticholinergic Burden (ACB) score.
Medical Treatment Options
Discuss these options with your prescribing physician. This information is educational, not medical advice.
Cognitive Rehabilitation / Occupational Therapy
Cancer-specific cognitive rehab program. Compensatory strategies (external memory aids, organizational systems), process training, and return-to-work support.
How it works ▼
Neuroplasticity-based recovery. Compensation for specific deficits identified on neuropsych testing.
Evidence: Moderate - growing evidence for cancer-specific cognitive rehab programs.
Source: NCCN Survivorship Guidelines
Psychostimulants (if appropriate)
Methylphenidate or modafinil may be considered for persistent fatigue-related cognitive impairment. Specialist-led.
How it works ▼
Increases dopamine and norepinephrine in prefrontal cortex, improving attention and processing speed.
Evidence: Low-Moderate - some evidence for cancer-related fatigue/cognition. Not routinely recommended.
Source: Cochrane psychostimulants for cancer fatigue
Supplements — What the Evidence Says
Supplements are adjuncts, not replacements for lifestyle changes. Discuss with your healthcare provider.
Omega-3 Fatty Acids
Dose: 2-3g EPA+DHA daily
Exercise and sleep improvement have stronger evidence. Omega-3s may support but shouldn't replace rehab.
How it works ▼
Anti-neuroinflammatory. Supports myelin repair and BDNF expression. May protect against chemotherapy-induced neurotoxicity.
Evidence: Low-Moderate - some preclinical evidence for neuroprotection. Safe as adjunct.
Orchard et al., Neurosci Biobehav Rev, 2017
Psychological Support and Therapy
Cognitive rehabilitation (OT-led). Neuropsychology for targeted assessment. Cancer survivorship program. If adjustment difficulty → cancer-specific counseling.
Quick Reference
Quick Win
Complete the FACT-Cog (Functional Assessment of Cancer Therapy - Cognitive Function) questionnaire. Track cognitive symptoms on a daily scale of 1-10. Share with your oncology team - most cancer centers now have survivorship programs that address cognitive symptoms.
Wagner et al., FACT-Cog validation; NCCN Survivorship Guidelines
Not sure this is your cause?
Brain fog can have many causes. The story analyzer can help narrow down what pattern fits best for you.
About This Page
Written by
Dr. Alexandru-Theodor Amarfei, M.D.Medical reviewer and clinical content lead for the What Is Brain Fog cause library
Research methodology
Evidence-based approach using peer-reviewed sources
View our evidence grading standardsLast updated: . We review our content regularly and update when new research emerges.
Important: This content is for educational purposes only and does not replace professional medical advice. Consult a qualified healthcare provider for diagnosis and treatment.
Claim-Level Evidence
- [C] Pattern-focused visual summary for Chemobrain intended to support structured, non-diagnostic investigation planning. low/validated
- [B] chemobrain: Schmitz et al., CA Cancer J Clin, 2019 - Exercise is medicine in oncology. medium/validated