DecisionDx®-Melanoma's i31-SLNB Outperforms MIA Nomogram in Identifying Patients Who May Safely Forgo Sentinel Lymph Node Biopsy

Rhea-AI Summary

Castle Biosciences (Nasdaq:CSTL) reported prospective, multicenter DECIDE study results showing its DecisionDx-Melanoma i31-SLNB risk prediction outperformed the MIA nomogram for sentinel lymph node (SLN) positivity in cutaneous melanoma.

In 912 patients, i31-SLNB low-risk cases had 2.6% observed SLN positivity vs 5.8% for MIA; overall AUC was 0.74 vs 0.61 (p=0.001).

Positive

• Prospective multicenter DECIDE study analyzed 912 melanoma patients considering SLNB
• i31-SLNB low-risk group had 2.6% SLN positivity vs 5.8% for MIA nomogram
• MIA nomogram did not identify patients below 5% NCCN SLN positivity threshold
• Discordant low-risk i31-SLNB group showed 2.8% SLN positivity vs 11.5% for MIA low-risk group
• i31-SLNB showed higher discriminative performance than MIA (AUC 0.74 vs 0.61; p=0.001)
• Results align with prior multicenter data, adding prospective evidence for DecisionDx-Melanoma use in SLNB decision-making

Negative

• None.

News Market Reaction – CSTL

+6.07%

4 alerts

+6.07% News Effect

+$42M Valuation Impact

$735.50M Market Cap

0.4x Rel. Volume

On the day this news was published, CSTL gained 6.07%, reflecting a notable positive market reaction. Our momentum scanner triggered 4 alerts that day, indicating moderate trading interest and price volatility. This price movement added approximately $42M to the company's valuation, bringing the market cap to $735.50M at that time.

Data tracked by StockTitan Argus on the day of publication.

Market Context

The stock moved +6.1% in the session following this news. A strong positive reaction aligns with evi...

Analysis

The stock moved +6.1% in the session following this news. A strong positive reaction aligns with evidence that i31-SLNB improves SLN risk discrimination, using a 912-patient prospective cohort and lowering observed low-risk positivity to 2.6%. Net insider activity has recently shown Net Selling, a potential overhang.

Key Figures

Low-risk SLN positivity (i31-SLNB): 2.6% Low-risk SLN positivity (MIA nomogram): 5.8% NCCN low-risk threshold: 5% +5 more

8 metrics

Low-risk SLN positivity (i31-SLNB) 2.6% Observed SLN positivity rate for patients classified low risk by i31-SLNB

Low-risk SLN positivity (MIA nomogram) 5.8% Observed SLN positivity rate for low-risk group per MIA nomogram

NCCN low-risk threshold 5% NCCN guideline threshold below which SLNB can be avoided

Negative SLNB procedures 88% Proportion of SLNB procedures reported as negative in melanoma staging

SLNB complications 15% Approximate proportion of patients with surgery-associated SLNB complications

DECIDE study size 912 patients Patients considering SLNB enrolled in multicenter DECIDE study

Discordant low-risk (i31<5%, MIA≥5%) 2.8% Observed SLN positivity when i31-SLNB low risk, MIA higher risk

Discordant low-risk (MIA low, i31 high) 11.5% Observed SLN positivity when MIA low risk, i31-SLNB higher risk

Historical Context

5 past events · Latest: Jun 23 ()

5 events

Date	Event	Sentiment	24h Move	Catalyst
Jun 23	Management recognition		+0.8%	CFO recognized as a 2026 CFO Awards honoree for financial leadership.
Jun 16	Product adoption		-1.0%	TissueCypher test surpasses 100,000 clinical orders in Barrett’s esophagus.
May 13	Conference presentation		-2.6%	Company to present overview at 2026 Jefferies Global Healthcare Conference.
May 12	Industry award		-2.1%	AdvanceAD-Tx test receives 2026 MedTech Breakthrough genomics innovation award.
May 06	Earnings report		-22.3%	Q1 2026 results with updated full-year guidance and core test growth metrics.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Key Terms

sentinel lymph node biopsy, nomogram, gene expression profile, p=0.001

4 terms

sentinel lymph node biopsy medical

"patients with melanoma may safely avoid SLNB and which should consider having the surgery"

A sentinel lymph node biopsy is a surgical procedure that removes and tests the first lymph node(s) that drain fluid from a tumor to see if cancer has spread. Think of it as checking the first security checkpoint after a breach; a negative result often means less extensive surgery and lower treatment costs, while a positive result can change therapy, prognosis, regulatory decisions and market demand for related diagnostics and treatments, making it important to investors.

nomogram medical

"outperforms the MIA nomogram in identifying patients at low and high risk"

A nomogram is a chart that turns multiple numbers into a single visual score or probability, letting you estimate outcomes by lining up values on several scales—think of it like a slide rule or infographic for calculations. Investors encounter nomograms in medical and risk reports because they make complex statistical models tangible, helping to judge likelihoods (such as treatment success or project risk) that can affect valuation and decision-making.

gene expression profile medical

"integrates the 31-gene expression profile (31-GEP) score with clinicopathologic factors"

A gene expression profile is a snapshot of which genes in a cell or tissue are switched on and how strongly they are producing their products, like a theater marquee showing which plays are running and how popular each is. For investors, these profiles matter because they can indicate whether a drug or diagnostic is likely to work, reveal which patient groups will benefit, and reduce development time and risk—factors that influence a biotech company’s value and commercial prospects.

p=0.001 technical

"greater discriminative performance than the clinicopathologic-only MIA nomogram (AUC=0.74 vs. 0.61; p=0.001)"

p=0.001 means the observed result would happen by random chance about 0.1% of the time if there were no real effect. Think of flipping a coin and getting an unusually long streak — a p-value this small suggests the streak is unlikely to be random. For investors, it signals strong statistical support behind a claim or study finding, but it does not measure how large or practically important the effect is, nor does it guarantee future outcomes.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Newly published prospective study shows DecisionDx-Melanoma's i31-SLNB test result more accurately identifies patients at low and high risk of sentinel lymph node (SLN) positivity than the Melanoma Institute Australia (MIA) nomogram

Patients classified as low risk by the i31-SLNB result had a 2.6% observed SLN positivity rate, falling well below the National Comprehensive Cancer Network (NCCN) 5% threshold used to consider avoiding sentinel lymph node biopsy (SLNB), compared with a 5.8% observed positivity rate for the MIA nomogram

FRIENDSWOOD, Texas, June 25, 2026 /PRNewswire/ -- Castle Biosciences, Inc. (Nasdaq: CSTL), a company improving health through innovative tests that guide patient care, today announced the publication of a prospective, multicenter study in Dermatology and Therapy demonstrating that DecisionDx-Melanoma's integrated sentinel lymph node biopsy test result (i31-SLNB) outperforms the MIA nomogram in identifying patients at low and high risk of SLN positivity, supporting more informed SLNB decision-making for patients with cutaneous melanoma (CM).¹ This is the second multicenter study showing that the i31-SLNB result outperforms the MIA nomogram in assessing SLN positivity risk.²

"Many clinicians are familiar with nomograms that estimate risk of sentinel lymph node positivity using clinicopathologic features alone, yet current guidelines acknowledge limitations in their performance at lower risk thresholds," said Rohit Sharma, M.D., FACS, lead author of the study and surgical oncologist at Marshfield Clinic Health System in Marshfield, Wisconsin. "Because of this, accurately identifying which patients are unlikely to have sentinel lymph node involvement remains an important challenge in melanoma care. The study findings demonstrate that incorporating tumor biology through DecisionDx-Melanoma's i31-SLNB test result can improve risk assessment, helping clinicians better distinguish which patients with melanoma may safely avoid SLNB and which should consider having the surgery."

Key findings from the study include:

• Patients classified as low risk by the i31-SLNB had an observed SLN positivity rate of 2.6% — below the 5% NCCN threshold when considering avoidance of SLNB — compared with 5.8% for the MIA nomogram. The MIA nomogram failed to identify patients with SLN risk below the 5% threshold.
• The i31-SLNB also outperformed the MIA nomogram when analyzing discordant risk classifications. Specifically, patients classified as low risk (less than 5%) by the i31-SLNB but higher risk (greater than or equal to 5%) by the MIA nomogram had an actual SLN positivity rate of 2.8%. Conversely, patients classified as low risk by the MIA nomogram but high risk by the i31-SLNB had an actual SLN positivity rate of 11.5%.

SLNB plays an important role in melanoma staging by helping determine whether melanoma has spread to nearby lymph nodes. However, up to 88% of SLNB procedures are negative and approximately 15% of patients experience surgery-associated complications. Current NCCN CM Guidelines recommend avoiding SLNB when the likelihood of SLN positivity is less than 5%, considering the procedure when risk is between 5% and 10%, and offering SLNB when risk exceeds 10%. These thresholds create a need for tools that can more accurately identify patients who may safely avoid the procedure while appropriately identifying those at higher risk.

The study, titled "Comparing the i31-SLNB and the MIA Nomogram for Sentinel Lymph Node Biopsy Positivity Prediction in Cutaneous Melanoma: A Prospective Cohort Analysis," evaluated 912 patients considering SLNB enrolled in the multicenter DECIDE study and directly compared the performance of DecisionDx-Melanoma's i31-SLNB result, which integrates the 31-gene expression profile (31-GEP) score with clinicopathologic factors, with the MIA nomogram, which estimates SLN positivity risk using clinicopathologic factors alone.

The study found that patients undergoing SLNB classified as low risk by the i31-SLNB (less than 5% predicted risk of SLN positivity) had an observed SLN positivity rate of 2.6%, showing concordance with predicted results. Patients predicted to have less than 5% risk of SLN positivity by the MIA nomogram had an observed positivity rate of 5.8%, showing discordance with predicted results; the MIA nomogram failed to identify patients below the 5% NCCN threshold used to consider avoiding SLNB.

The study also examined patients whose risk predictions were discordant between the two approaches. Among patients classified as low risk (less than 5%) by the i31-SLNB but higher risk (greater than or equal to 5%) by the MIA nomogram, the observed SLN positivity rate was only 2.8%. Conversely, among patients classified as low risk by the MIA nomogram but higher risk by the i31-SLNB, the observed positivity rate was 11.5%, demonstrating that the i31-SLNB again outperformed the MIA nomogram.

Overall, the i31-SLNB result demonstrated greater discriminative performance than the clinicopathologic-only MIA nomogram (AUC=0.74 vs. 0.61; p=0.001), indicating improved accuracy in identifying patients at both low and high risk of SLN positivity.

These findings are consistent with previously published evidence, including Zakria et al, 2022, a retrospective, multicenter study that also showed DecisionDx-Melanoma outperformed the MIA nomogram.² They also add to the growing body of prospective evidence supporting the use of DecisionDx-Melanoma to inform SLNB decision-making and further demonstrate the value of integrating tumor biology with clinicopathologic factors to improve risk assessment and support more informed, risk-aligned care for patients with CM.^3-6

About DecisionDx-Melanoma
DecisionDx-Melanoma is a gene expression profile (GEP) test designed to analyze tumor biology to deliver a personalized risk assessment for patients with stage I–III cutaneous melanoma, enhancing risk stratification beyond American Joint Committee on Cancer (AJCC) staging alone. By combining molecular insights with select clinicopathologic features, the test provides two distinct outputs: a personalized risk of sentinel lymph node (SLN) positivity and a personalized risk of recurrence and/or metastasis. This clinically actionable information is designed to help guide risk-aligned patient management decisions, including SLN biopsy consideration, follow-up intensity, imaging and referrals.

DecisionDx-Melanoma is supported by more than 50 peer-reviewed publications, including prospective studies and meta-analyses, and was developed in collaboration with more than 100 leading U.S. institutions. The test has been clinically validated in more than 10,000 patient samples, ordered more than 240,000 times since launch, and has been shown to be associated with improved patient survival. Learn more at www.CastleBiosciences.com.

About Castle Biosciences
Castle Biosciences (Nasdaq: CSTL) is a leading diagnostics company improving health through innovative tests that guide patient care. With a primary focus in dermatologic and gastroenterological disease, we develop personalized, clinically actionable solutions that help improve disease management and patient outcomes.

We put people first—empowering patients and clinicians and informing care decisions through rigorous science and advanced molecular tests that support more confident treatment planning. To learn more, visit www.CastleBiosciences.com and connect with us on LinkedIn, Instagram, Facebook and X. 

DecisionDx-Melanoma, DecisionDx-CMSeq, i31-SLNB, i31-ROR, DecisionDx-SCC, MyPath Melanoma, AdvanceAD-Tx, TissueCypher, Esopredict, DecisionDx-UM, DecisionDx-PRAME and DecisionDx-UMSeq are trademarks of Castle Biosciences, Inc.

Forward-Looking Statements
This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, which are subject to the "safe harbor" created by those sections. These forward-looking statements include, but are not limited to, statements concerning: the ability of DecisionDx-Melanoma's i31-SLNB test to (i) accurately identify patients at low and high risk of SLN positivity and support more informed SLNB decision-making for patients with cutaneous melanoma; (ii) help clinicians distinguish which patients with melanoma may safely avoid SLNB and which are more likely to benefit from the procedure; (iii) generate a personalized likelihood of SLN positivity to support risk-aligned shared decision-making consistent with NCCN guideline thresholds; and (iv) improve risk assessment and support more informed, risk-aligned care for patients with CM. The words "designed," "may," "can," "supporting," "helping," "intended to" and similar expressions are intended to identify forward intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements that we make. These forward-looking statements involve risks and uncertainties that could cause actual results to differ materially from those in the forward-looking statements, including, without limitation: subsequent study or trial results and findings may contradict earlier study or trial results and findings or may not support the results obtained in these studies, including with respect to the discussion of our tests in this press release; actual application of our tests may not provide the aforementioned benefits to certain patients; and the risks set forth under the heading "Risk Factors" in our Annual Report on Form 10-K for the year ended December 31, 2025, and our subsequent Quarterly Reports on Form 10-Q, each as filed or to be filed with the SEC, and in our other filings with the SEC. The forward-looking statements are applicable only as of the date on which they are made, and we do not assume any obligation to update any forward-looking statements, except as may be required by law.

1. Sharma, R., Kulkarni, R.P., Essner, R. et al. Comparing the i31-SLNB and the MIA Nomogram for Sentinel Lymph Node Biopsy Positivity Prediction in Cutaneous Melanoma: A Prospective Cohort Analysis. Dermatol Ther (Heidelb) (2026). https://doi.org/10.1007/s13555-026-01819-6
2. Zakria D, Brownstone N, Rigel D. The integrated 31-gene expression profile (i31-GEP) test for cutaneous melanoma outperforms a clinicopathologic-only nomogram at identifying patients who can forego sentinel lymph node biopsy. J Skin. 2022;6(6):463-473. doi:10.25251/skin.6.6.3
3. Yamamoto M, Sickle-Santanello B, Beard T, et al. The 31-gene expression profile test informs sentinel lymph node biopsy decisions in patients with cutaneous melanoma: results of a prospective, multicenter study. Curr Med Res Opin. 2023;39(3):417-423. doi:10.1080/03007995.2023.2165813
4. Guenther JM, Ward A, Martin BJ, et al. A Prospective, Multicenter Analysis of Recurrence-Free Survival After Sentinel Lymph Node Biopsy Decisions Influenced by the 31-GEP. Cancer Med. 2025;14(7):e70839. doi:10.1002/cam4.70839
5. Guenther JM, Ward A, Martin B, et al. A prospective, multicenter analysis of the integrated 31-gene expression profile test for sentinel lymph node biopsy (i31-GEP for SLNB) test demonstrates reduced number of unnecessary SLNBs in patients with cutaneous melanoma. World J Surg Oncol. 2025 Jan 3;23(1):5. doi: 10.1186/s12957-024-03640-x
6. Beard T, Guenther JM, Leong SP, et al. The integrated 31-gene expression profile test identifies low-risk patients with cutaneous melanoma who can forego the SLNB procedure: results from a prospective, multicenter trial. Future Oncol. Published online March 13, 2026. doi: 10.1080/14796694.2026.2640227

Investor Contact:
Camilla Zuckero
czuckero@castlebiosciences.com

Media Contact:
Allison Marshall
amarshall@castlebiosciences.com

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SOURCE Castle Biosciences, Inc.

FAQ

What did Castle Biosciences (CSTL) announce about the DecisionDx-Melanoma i31-SLNB study on June 25, 2026?

Castle Biosciences announced prospective DECIDE study results showing the DecisionDx-Melanoma i31-SLNB test outperformed the MIA nomogram for predicting sentinel lymph node positivity. According to Castle Biosciences, the analysis included 912 cutaneous melanoma patients across multiple centers.

How does DecisionDx-Melanoma's i31-SLNB compare with the MIA nomogram in identifying low-risk melanoma patients (CSTL)?

DecisionDx-Melanoma's i31-SLNB classified low-risk patients with an observed 2.6% SLN positivity rate, versus 5.8% using the MIA nomogram. According to Castle Biosciences, i31-SLNB patients under 5% predicted risk stayed below the NCCN 5% threshold for considering SLNB avoidance.

What were the AUC results for i31-SLNB versus the MIA nomogram in Castle Biosciences' DECIDE study?

The i31-SLNB achieved an AUC of 0.74, compared with 0.61 for the MIA nomogram. According to Castle Biosciences, this statistically significant difference (p=0.001) indicates greater discriminative performance for identifying both low and high risk of sentinel lymph node positivity.

How did discordant risk classifications between i31-SLNB and the MIA nomogram affect observed SLN positivity rates for CSTL's test?

Patients low risk by i31-SLNB but higher risk by MIA had 2.8% SLN positivity, while those low risk by MIA but higher risk by i31-SLNB had 11.5%. According to Castle Biosciences, these discordant results favored i31-SLNB accuracy.

How might DecisionDx-Melanoma i31-SLNB influence sentinel lymph node biopsy decisions for melanoma (CSTL)?

The i31-SLNB test may help align SLNB decisions with NCCN risk thresholds by better identifying patients below 5% SLN positivity risk. According to Castle Biosciences, integrating 31-GEP tumor biology with clinicopathologic factors supports more risk-informed melanoma care.

Is the DECIDE study on DecisionDx-Melanoma i31-SLNB Castle Biosciences' first comparison with the MIA nomogram?

No, the DECIDE study is the second multicenter analysis showing i31-SLNB outperformed the MIA nomogram. According to Castle Biosciences, earlier retrospective work by Zakria et al. (2022) also reported superior DecisionDx-Melanoma performance in SLN positivity risk prediction.