SecProbe.io

July 17, 2025
Oguzhan Atay
Chief Executive Officer
BillionToOne, Inc.
1035 O’Brien Drive
Menlo Park, CA 94025
Re:BillionToOne, Inc.
Draft Registration Statement on Form S-1
Submitted June 20, 2025
CIK No. 0002070849
Dear Oguzhan Atay:
            We have reviewed your draft registration statement and have the following comments.
            Please respond to this letter by providing the requested information and either
submitting an amended draft registration statement or publicly filing your registration
statement on EDGAR. If you do not believe a comment applies to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.
            After reviewing the information you provide in response to this letter and your
amended draft registration statement or filed registration statement, we may have additional
comments.
Draft Registration Statement on Form S-1
Glossary, page ii
1.Please revise the terms included in the glossary to include a brief description of the
relevance of the terms to your operations. As an example only, we note that you
define cfDNA as "[c]ell free DNA released from tumor cells". Please briefly explain,
or include a cross reference to your disclosures on pages 4 and 117, the relevance of
cfDNA for modern precision medicine. Likewise, please explain the relevance
of polymerase chain reactions, and define methylation and sample accessioning.

July 17, 2025
Page 2
Prospectus Summary
Overview, page 2
2.We note your disclosure on page 48 that "[y]ou currently offer a number of genetic
tests, each of which is a laboratory developed test (LDT)". Please revise your
summary to prominently note, if true, that all of your current products are LDTs,
which are not subject to FDA regulatory approvals.
3.We note your disclosure that "[yo]ur superior technology platform has enabled [you]
to build category-defining prenatal and oncology products," and that "[you] have
established [y]ourselves as a leader in the prenatal testing market." Please revise to
discuss the metric upon which you base this statement that your technology platform
is superior and that you are a leader in the prenatal testing market. For example,
explain whether you are measuring by revenue or market share, or a combination of
various metrics. We refer to your disclosure on page 128 that "[you] are the second
largest prenatal genetics laboratory in the United States by revenue."
4.We note your disclosure that you estimate "an annual market opportunity of over
$100 billion in the United States alone," and that "[w]hile [y]our current products
already address an estimated annual market opportunity of over $20 billion in the
United States, [you] believe that [y]our R&D pipeline could eventually expand this
annual addressable market to over $100 billion." We also note your disclosure on
page 97 that the $100 billion figure is comprised of an addressable market of $1
billion for carrier screening, $1.5 billion for aneuploidy testing, $6 billion for therapy
selection, over $15 billion for therapy monitoring, over $30 billion for minimal
residual disease and over $50 billion for early detection. Please revise to provide a
detailed discussion of how you calculate each of these addressable market figures, and
discuss any material assumptions underlying these calculations, such as the price at
which you are able to sell your products and the available patient population. Please
also revise to clarify why you include products that have not yet been launched in
your total addressable market calculation. In your discussion, please also explain the
basis for your disclosure on page 97 that "[you] estimate the 14-gene version of
UNITY Fetal Risk Screen will expand the serviceable addressable market for UNITY
by 70%" and on page 128 that "[you] estimate that the [oncology] market is less than
20% penetrated today by all molecular diagnostics companies."
5.We note your disclosure on page 37 that "[you] have incurred significant losses since
[y]our inception. For the years ended December 31, 2023 and 2024, [you] incurred net
losses of $82.7 million and $41.6 million, respectively. As of December 31, 2024,
[you] had an accumulated deficit of $282.2 million." Please revise your prospectus
summary to discuss your significant losses and accumulated deficit for the periods
presented.
Our four pillars of differentiation, page 3
We note your disclosure that "[yo]ur revolutionary platform achieves absolute
quantification at the single molecule level, enabling [you] to: (i) accurately quantify
genetic targets by eliminating biases introduced from next-generation sequencing
(NGS); (ii) precisely measure and analyze intermediate biochemical reactions to
optimize the performance of [y]our assays; and (iii) reduce sequencing costs by 6.

July 17, 2025
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obtaining a higher quality signal at each genomic location analyzed." Please clarify
these biases that are eliminated from NGS, and explain how a higher quality signal
can reduce sequencing costs.
Our Superior Efficiency, page 4
7.We note your disclosure which describes your limited accumulated deficit as of
December 31, 2024 being a small fraction of the losses incurred by some of your
competitors. Please remove the comparative disclosure or revise to provide
substantiation for the statement.
Our solution and suite of products, page 6
8.We note your disclosure that "[you] intend to expand [y]our oncology test offerings
into testing of earlier stage cancer patients, including through MRD testing and
potentially for early cancer detection." Please revise to provide a more detailed
discussion of the current stage of development of each of your product candidates, and
note the expected timing for their commercialization. Please also disclose whether any
of the product candidates are expected to require FDA regulatory approvals.
Prenatal products, page 6
9.We note your graphic reflecting a brief description of your prenatal products. Please
revise to briefly describe the Aneuploidy NIPT + RhD NIPT product.
Risk Factors
If the government and other third-party payors fail to provide coverage and adequate payment
for our existing and future tests, our..., page 20
10.We note your disclosure that "[t]hird-party reimbursement for [y]our tests represents a
significant portion of [y]our revenue, and [you] expect government and commercial
third-party payors to continue to be [y]our primary source of payments." We also note
your disclosure that "third-party payor revenue for [y]our testing...constitutes the large
majority of [y]our revenue." Please disclose the percentage of your revenue
represented by third-party reimbursements for the financial periods presented.
11.We note your disclosure on page 21 that "[w]hile ACOG guidelines generally
acknowledge that NIPT is the most sensitive screening option for, and/or are generally
supportive of NIPT in, average-risk pregnancies in addition to high-risk
pregnancies...not all of [y]our current tests are covered under practice guidelines, and
[you] cannot predict whether [y]our future tests will be covered by such guidelines."
Please clarify which of your current tests are not covered under practice guidelines.
Our revenue may be adversely affected if we are unable to successfully obtain reimbursement
from the Medicare program and state Medicaid..., page 22
12.We note your disclosure that "[i]t is estimated that nearly half of all births in the
United States are to state Medicaid program beneficiaries. Each state’s Medicaid
program has its own coverage determinations related to [y]our testing, and several
state Medicaid programs do not provide coverage for [y]our testing." Please clarify
which state Medicaid programs do not provide coverage for your testing.

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We and the third parties with whom we work are subject to stringent and evolving U.S. and
foreign laws, regulations, and rules..., page 50
13.You disclose that your employees and personnel may use generative artificial
intelligence and machine learning to perform their work and that "[you] use AI/ML to
assist [you] in making certain decisions, which is regulated by certain privacy laws."
Please revise to further discuss the decisions for which you currently use AI/ML.
Use of proceeds, page 79
14.We note your disclosure that "[you] currently intend to use the net proceeds from this
offering, together with [y]our existing cash and cash equivalents, for working capital
and other general corporate purposes, including to fund [y]our growth, research and
development initiatives, technology development, working capital, and operating
expenses." Please revise to further discuss the use of the proceeds to fund your
growth, research and development initiatives, and technology development. Refer to
Item 504 of Regulation S-K.
Management's discussion and analysis of financial condition and results of operations
Our business model and key performance metrics, page 91
15.Please revise to define "Blended ASP," and explain how it is calculated.
Key factors affecting our results of operations and performance, page 92
16.We note your disclosure on page 93 that "[o]nce an ordering provider within a clinic
first starts to use [y]our tests, [you] often see expansion of [y]our tests to other
providers within the clinic. [You] believe that [y]our unique product offerings and
exceptional end-to-end service drive this adoption. [Yo]ur cohort analysis indicates
that the net test retention, as defined by the total number of tests that are received
from a cohort of clinics first onboarded in a particular quarter, even after accounting
for any account or provider churn, is over 100% after a year for the majority of
quarterly cohorts." Please revise to define "cohort" and further discuss your cohort
analysis, including an explanation of how it demonstrated net test retention.
17.We note your disclosure on page 93 that "[you] believe [y]our tests provide far higher
value than the Medicare Clinical Laboratory Fee Schedule (CLFS) rates established
for [y]our tests. For instance, in a peer-reviewed publication, the break-even price for
sgNIPT was estimated between $2,336 (healthcare cost-neutral price with better
outcomes) and $7,233 (equivalent cost of identifying one affected pregnancy vs.
sequential carrier screening). In comparison, the CLFS price for [y]our sgNIPT was
established at $879.47." Please revise to disclose the peer-reviewed publication, and
further explain why you estimated that the break-even price for sgNIPT should be
based on the healthcare cost-neutral price with better outcomes and/or the
equivalent cost of identifying one affected pregnancy vs. sequential carrier screening.
Key components of results of operations, page 97
We note your disclosure that "[t]he majority of [y]our revenue is derived from sales of
[y]our prenatal test, UNITY, and a smaller portion is derived from sales of [y]our
liquid biopsy oncology tests, Northstar," and that "[r]evenue is comprised of revenue 18.

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from [y]our sales of [y]our prenatal and oncology tests and [y]our strategic
partnership with Johnson & Johnson." Please revise to disclose the percentage of your
revenue derived from your prenatal tests as compared to your oncology tests, and your
strategic partnership with Johnson & Johnson.
Comparison of years ended December 31, 2023 and 2024
Revenue and gross margin, page 101
19.With regard to your 113% increase in revenue and your increase in gross margin from
24% to 53%, please address the following:
•Explain the reasons underlying the increase in tests processed and your increase in
average selling price per test.
•To the extent material, ensure you address how changes in payor mix impacted
your average selling price.
•Expand your disclosures to explain how the increase in revenue impacted gross
margin. To the extent that it relates to your composition of fixed versus variable
costs, provide a discussion of the degree to which cost of revenue is fixed versus
variable.
•Address whether there is any related trend information underlying your revenue
and gross margin results. Refer to Item 303(b)(2)(ii) of Regulation S-K.
Liquidity and capital resources
Oberland Capital note purchase agreement, page 106
20.Please expand your disclosures to address the following:
•Expand your disclosures to quantify the royalty participation payments and clarify
when they become applicable and payable. In this regard, we note you earned
more than $100 million in revenue during the year ended December 31, 2024.
•Quantify the internal rate of return Oberland will earn over the course of the loan.
•Clarify whether or not you are in compliance with each material financial
covenant.
See Sections I.D and IV.C of the SEC Interpretive Release No. 33-8350.
Business
Our Product Portfolio, page 131
We note that you refer to various studies, publications and collaborations throughout
this section. As an example only, we note your disclosure on page 130 that
"[you] have demonstrated the analytical and clinical validity, as well as the clinical
utility, of [y]our Northstar Select test through rigorous reviews," and that "[i]n
validation studies, Northstar Response showed a consistent ability to detect
quantitative changes in tumor fraction across more than 10 different cancer types, in
some cases as much as six months earlier than indicated by imaging scans. Northstar
Response has been analytically and clinically validated in three peer-reviewed
publications, including in collaborations with the University of California, San Diego
and the University of Florida." We also note your disclosure on page 143 that
"[you] have extensive publications on [y]our smNGS platform and products". Please
revise to discuss each of these studies, publications and collaborations in further 21.

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detail. In particular, please disclose the date(s) and location(s) of the studies and trials,
the sponsor(s), the number of participants, including how participants were selected,
the results of the studies and trials, including how results were measured, key
assumptions, any serious adverse events, and whether statistical significance was
demonstrated, including supporting p-values, as appropriate. Please also disclose
whether any of the parties involved, including the sponsors in the studies and/or trials,
are affiliates or partners of BillionToOne. Consider providing the disclosures in
tabular format for ease of reference.
22.We note your disclosure throughout this section referring to the demonstrated
analytical and clinical validity of your products. For example, we note your disclosure
on page 130 that "[you] have demonstrated the analytical and clinical validity, as well
as the clinical utility, of [y]our Northstar Select test through rigorous reviews." You
also state on page 134 that the "UNITY Fetal Risk Screen’s accuracy has been
validated in multiple peer-reviewed studies." Please revise to define analytical and
clinical validity and clarify how you have demonstrated the validity and utility of your
products without receipt of FDA or equivalent regulatory approvals. Safety and
efficacy are determinations that are solely within the authority of FDA or similar
foreign regulators. Where applicable, please clarify that certain of your products have
not been approved by the FDA or or similar foreign regulators and remove any
statements of safety and efficacy for such products. You may present clinical trial end
points and objective data resulting from trials or studies without concluding efficacy.
23.Please revise the table illustrating the UNITY Fetal Risk Screen's testing menu to
further explain the two columns included in the table.
UNITY Fetal Antigen CTA NIPT, page 136
24.We note your disclosure that "[i]n December 2023, [you] announced a global
partnership with Johnson & Johnson to provide [y]our UNITY Fetal Antigen clinical
trial assay (CTA) in their AZALEA Phase 3 clinical tr