Washington, D.C. 20549  
Pursuant to Section 13 or 15(d)
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Date of report (Date of earliest event reported): January 7, 2019
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Item 7.01. Regulation FD Disclosure.
Beginning on January 7, 2019, representatives of Guardant Health, Inc. (the “Company”) intend to make presentations at investor conferences and in other forums and these presentations may include the information contained in Exhibit 99.1 attached to this Current Report on Form 8-K. A copy of certain of the presentation slides containing such information that may be disclosed by the Company is attached as Exhibit 99.1 to this report and the information set forth therein is incorporated herein by reference and constitutes a part of this report.
The information included under Item 7.01 in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section, nor shall it be deemed to be incorporated by reference into any filing of the Company under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.
Item 8.01. Other Events.
On January 7, 2019, the Company announced that its LUNAR assay, a new blood-based assay intended to detect early-stage cancer and recurrence of disease, is now available for research use by biopharmaceutical and academic researchers.
The assay was developed under the Company’s LUNAR program for early-stage detection and recurrence monitoring. It is based on biological insights from more than 80,000 cancer patients tested with Guardant360, the Company’s comprehensive liquid biopsy test, as well as learnings from whole-genome sequencing liquid biopsy data.
Multiple top-tier academic research networks and biopharmaceutical companies will utilize the LUNAR assay in studies involving adjuvant therapy decision-making, recurrence monitoring, and screening for early-stage cancer. The Company expects the clinical version of the test for use in prospective studies to launch in the second half of 2019.
Forward-Looking Statements
This Current Report on Form 8-K contains forward-looking statements within the meaning of federal securities laws, such as statements about the expected timing for a clinical launch of the LUNAR assay. Such statements reflect the Company’s current expectations, forecasts and assumptions. Actual results may vary materially from forward-looking statements due to risks, uncertainties and other factors, known and unknown to the Company as of the date hereof, such as those discussed in the Company’s filings with the Securities and Exchange Commission, including under the caption “Risk Factors” in its Quarterly Report for the period ended September 30, 2018 and in its subsequent filings with the Securities and Exchange Commission. The forward-looking statements in this Current Report on Form 8-K are based on information available to the Company as of the date hereof, and should not be relied upon as representing the Company’s views as of any date subsequent to the date of this press release. The Company disclaims any obligation to update any forward-looking statements, except as required by law.
Item 9.01. Financial Statements and Exhibits.
Exhibit No.

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
Date: January 7, 2019
/s/ Helmy Eltoukhy
Helmy Eltoukhy
Chief Executive Officer

Guardant Health Investor Presentation January 2019

Safe harbor statement This presentation contains “forward-looking statements,” which are statements related to future events that by their nature address matters that are uncertain. All forward-looking information is inherently uncertain and actual results may differ materially from assumptions, estimates or expectations reflected or contained in the forward-looking statements as a result of various factors. For details on the uncertainties that may cause our actual results to be materially different than those expressed in our forward-looking statements, please refer to our reports filed with the Securities and Exchange Commission, including our quarterly report on Form 10-Q for the period ended September 30, 2018. Forward-looking statements address our expected future business, financial performance, financial condition as well as results of operations, and often contain words such as “intends,” “estimates,” “anticipates,” “hopes,” “projects,” “plans,” “expects,” “seek,” “believes,” "see," “should,” “will,” “would,” “target,” and similar expressions and the negative versions thereof. Such statements are based only upon our current expectations. Any forward-looking statement speaks only as of the date made. Reliance should not be placed on forward-looking statements because they involve known and unknown risks, uncertainties and other factors which may cause actual results, performance or achievements to differ materially from those expressed or implied. Forward-looking statements include statements that address activities, events or developments that we expect, believes or anticipate will or may occur in the future. Forward-looking statements are based on our experience and perception of current conditions, trends, expected future developments and other factors we believe are appropriate under the circumstances and are subject to numerous risks and uncertainties, many of which are beyond our control. We undertake no obligation to publicly update or revise any forward-looking statements to reflect new information or future events or otherwise unless required by law. 2

The mission of Guardant Health is to conquer cancer with data Expanding precision oncology to all stages of disease through easier access to cancer’s underlying molecular information Market leading comprehensive 6,000+ 50+ 80,000+ 90%+94% liquid biopsy oncologists biopharma tests ordered GrowthRevenue in 1Hgrowth 20181 companies vs. 1H 2017 Therapy selection Recurrence monitoring Early detection - 1 - 2 1 YTD as of September 30, 2018 compared to nine-months ended 2017 3

Tumors shed cell-free nucleic acids into the blood at low concentrations Guardant proprietary technology unlocks these tumor signals from a simple blood draw TUMOR 4

Focused on expanding the scope of precision oncology Therapy Selection Recurrence Monitoring Early Detection Late-stage cancer patients Cancer survivors Asymptomatic individuals No Tissue Available Limitations of Tissue Availability and High False Positive Rate LimitationsCurrent Exhaustion Approachesof Current Symptomatic Intervention Approaches Delay in Care Low Compliance 8% 56% 38% Patient of advanced NSCLC patients are of colon cancer patients referred of NSCLC patients are diagnosed Impact tested for biomarkers in line with for disease recurrence have not with early stage disease the NCCN Guidelines had a recurrence Our - 1 - 2 Solution Commercial 2014 Commercial 2017 for research use Rebecca L. Siegel, Cancer Statistics, 2018, A Cancer Journal for Clinicals, Gutierrez et al. 2017 Clinical Lung Cancer, PLOS ONE | DOI:10.1371/journal.pone.0171810 5

Realizing the $35B+ U.S. opportunity requires delivering the right information for the right intervention for the right patient population U.S. Patient Advanced-Stage Cancer Cancer Survivors Asymptomatic, Hi-Risk Population ~700 K ~15 million ~35 million Screening & Early Therapy Selection Recurrence Monitoring Information Detection - 1 - 2 Targeted & Immuno- Neoadjuvant, Adjuvant, or Curative or Preventative Intervention oncology therapies Curative 50+ biopharma companies U.S. Market ~$6B ~$15B ~$18B Size Source: CDC Statistics; US Census; American Cancer Society, Cancer Facts and Statistics; SEER; Rebecca L. Siegel, Cancer Statistics, 2018, A Cancer Journal for Clinicals, 68:7; Piper Jaffray, Liquid Biopsy Report, Cowen Equity Research, Foundation Medicine, dated March 18, 2018; CDC, Viral Hepatitis and Liver Cancer report. 6 Note: Market sizing based on Guardant Health internal analysis.

Digital sequencing platform Patented proprietary technology for unlocking cancer’s signals from blood G U A R D A N T D I G I TA L S E Q U E N C I N G P L AT F O R M High- Next Learning - 2 Efficiency Generation Bioinformatics - 1 Chemistry Sequencing Engine TCAGCA GTGCGCTA AGCTA TGCATG GCATCG GTGTG Biochemistry Genomic Signal Bioinformatics sequencing processing Process engineering Machine learning 6 0 + P A T E N T S I S S U E D A N D 1 3 0 + P E N D I N G P A T E N T A P P L I C A T I O N S 7

Digital Sequencing Platform: underlying technology Guardant Digital Sequencing Biochemistry and Error Reduction High-Efficiency Biochemistry Learning Bioinformatics Engine High- Learning 1000X reduction in Efficiency 2-3X conversion higher efficiency Bioinformatics sequencing error than other methods rate Chemistry Engine Digital Sequencing unlocks signal from noise across all 4 classes of genomic alterations and MSI Standard NGS Guardant Digital Sequencing 100% 100% 10% 10% Noise lowered by >3 orders of magnitude 1% SNV 1% 0.1% 0.1% 0.01% 0.01% 8 Source: Odegaard et al. CCR, 2018.

Liquid biopsy for therapy selection in advanced cancer Market leading Comprehensive Liquid Biopsy Guideline-complete clinical results for advanced >2MB footprint panel tailored for immuno- solid tumors in less than 7 days oncology and targeted therapy development 9

Guardant360 clinical data highlights 42 98 295 Clinical Peer-reviewed Scientific studies Publications abstracts 10

JAMA Oncology: Support for a blood first paradigm in NSCLC University of Pennsylvania study of 323 NSCLC Patients tested with Guardant360 “These results [Aggarawal et al], combined with the patient 2x satisfaction with the relative ease 44% ~90% of providing blood rather than a solid tissue sample, suggest a clinical strategy of pursuing plasma NGS first, then tissue of eligible patients Concordance at The number of patients didn’t get results diagnosis found with targetable NGS if plasma NGS cannot from tissue biopsy reported for mutations 82 patients detect relevant mutations.” Guardant360® with Guardant360® + and tissue testing tissue testing versus 47 – Gyawali B and West J, JAMA patients with tissue Oncology, 2018 testing alone 11

NILE: Guardant360 vs standard of care in 1st-line NSCLC Readout of primary endpoint expected in 1H 2019 300 NSCLC Patients Prospective, Multi-Center Trial Standard of Care Tissue Testing + Detection of NCCN Detection of NCCN Biomarkers with Tissue VS Biomarkers with Testing 12

Establishing a blood first paradigm in advanced cancer Guardant360 Pan-Cancer NILE FDA Approval Medicare Coverage Interim Readout PMA Submission Post FDA Approval via 1H 2019 1H 2019 the NGS NCD <7-day TAT 13

Medicare and strong private payer coverage today and opportunity for increased coverage post FDA approval Q2 2016 Q3 2017 Q4 2017 Q1 2018 Q3 2018 Q4 2018 Total Covered 700K 3.7M 6.9M 21.9M 89.9M 115.3M Lives (Estimated) Estimates for Q2 2016 through Q4 2019 are as of 1/04/2019 14

Biopharma is a significant portion of $6B therapy selection market 1200+ targeted therapy and I-O programs 130,000+ patients ~$4 Billion Biopharmaceutical U.S. Market Opportunity Estimates ($mm) Clinical 50+ Opportunity ~$2 Billion $250 $2,120 pharma $320 Biopharmaceutical partners Opportunity $370 $1,180 Prospective Retrospective CDx Commercial Total Sources: SEER; Rebecca L. Siegel, Cancer Statistics, 2018, A Cancer Journal for Clinicians, 68:7; Piper Jaffray, Liquid Biopsy Report. Guardant Health Biopharma, Global Data, June 2017;; Campbell (Meyerson) and TCGA 2016 Nature Genetics. 15 Note: Market sizing based on Guardant Health internal analysis.

Partnership with AstraZeneca to develop multiple plasma- based companion diagnostic tests 16

AstraZeneca Partnership: Guardant found more patients who may benefit from combination immunotherapy Evaluable Patients for TMB analysis Guardant TMB High Overall Survival 809 460 Tissue TMBEvaluable TMB Patients Annals of Oncology, Volume 29, Issue suppl_10, 1 December 2018 17

To develop affordable multi-cancer assays for early detection and recurrence monitoring Lung CRC Breast Ovarian 18

Commercial engine as a significant R&D force multiplier 80,000+ sample data & biobank Leveraging data, biobank and insights produced by commercial engine can create technology compounding effect - 1 19

The challenges of detecting residual disease using cell-free DNA with high sensitivity and high specificity Detection Challenges Genomic Sensitivity Signatures • Genomic signatures alone max out at~50% sensitivity for early cancer TUMOR + Specificity • Non-tumor sources of biological noise, such as CHIP, can increase Epigenomic difficulty of highly specific Signatures detection • Using prior knowledge of tumor MICRO- tissue to filter out such noise is ENVIRONMENT clinically challenging 20

Introducing the assay LUNAR now available for research use by biopharmaceutical and academic researchers Genomic Alterations Biological Noise Filter LUNAR 80,000 ctDNA TEST RESULT Whole Signal Integration Genome ctDNA Sequencing Tests present / absent Epigenomic Epigenomic Signatures Classifier Launched for RUO in Q4’18 and planned CLIA launch for prospective studies in 2H’19 21

LUNAR Assay Performance Hybrid genomics and epigenomics approach can improve sensitivity to early stage cancers Late-stage • Assay reportable range down to 0.01% for genomic alterations • High quantitative correlation between genomic and epigenomic signal components • Epigenomic component detects Genomic Genomic Alterations Early-stage many samples that were negative with genomics-only Normal component Epigenomic Signatures Internal Guardant Health data 22

- 1: Selecting patients with residual disease for adjuvant therapy may improve outcomes in multiple cancers Breast Lung CRC Ovarian e.g., Herceptin No well-defined standard for accurately Nearly 50% reduction selecting patients for adjuvant therapy in risk of recurrence(1) (1) N Engl J Med 2005;353:1659-72. 23

- 1: Detection of post-op residual disease in CRC and NSCLC Study of colorectal cancer patients over 5 years Study of resected early-stage NSCLC • Prospective, comprehensive profiling 19.4 months follow-up • Retrospective surgical CRC study with 5 year follow-up Design • ctDNA assessment of MRD pre- and post-op at 4 weeks and until Design • Patients going through curative-intent hepatectomy recurrence ) s t n e i t a 4wk ctDNA not detected p f o % ( l a v i v r u s e e r f e c 4wk ctDNA detected n e HR 4.68 (1.55 - 14.16) r r p = 0.003 by log-rank u c e R Months Months • Somatic panel with classifier to filter non-tumor variants • ctDNA detected in 84% of pre-op samples • ctDNA detected in 69% evaluable patients prior to/at time of Results • All patients with detected ctDNA using LUNAR assay post-op Results recurrence relapsed (48% sens / 100% spec) • ctDNA detected post-op four months earlier than radiographic recurrence Overman (Kopetz) et al. Jun 2018 J Clin Oncol 36, 2018 (suppl; abstr 12044) Lam (Heymach ) et al. Sep 2018 WCLC 24

- 2: Addressing need for improved early cancer detection Pilot data has demonstrated strong performance in early detection of lung cancer LUNAR-2 Lung Sensitivity by Stage Sensitivity Sensitivity at around 98% specificity STAGE 1 STAGE 2 Note: The pilot data presented here may be impacted by small sample sizes, non-ideally matched and unblinded controls, and potentially other confounding factors. Further studies are 25 required to verify the presented performance.

Strong financial profile Revenues ($000’s) Sample Volumes (1) Gross Profit Margin (2) BioPharma Clinical 27,981 $57,766 49.3%49.3% +33% +100% +94% 20,960 20,644 $29,840 24.7%24.7% 17,304 7,337 3,656 2017 2018 2017 2018 2017 2018 Q3 YTD Q3 YTD Q3 YTD Q3 YTD Q3 YTD Q3 YTD (1) Clinical volume excludes 352 and 1,382 tests in the first nine months of 2018 and 2017, respectively, from a customer that in March 2018 began processing tests in-house 26 (2) Gross profit margin = gross profit / total revenue Gross profit = Total revenue – Cost of precision oncology testing – Cost of development services

Significant opportunities to drive future growth -2 -1 International Increased expansion Continued adoption of COGS and CGP Blood-First opex Volume Growth leverage FDA approval Medicare NCD OMNI (pan-cancer) Commercial payer Pharma CDx reimbursement Medicare LCD tailwinds (lung) Near-term drivers Long-term drivers 27