CSTL · Castle Biosciences

The thesis

Castle Biosciences is rated Medium, modestly more likely than not to beat the S&P 500 over three months. It raised 2026 revenue guidance to $385–395 million on 5 November 2026 and kept its 50–52% volume growth plan for TissueCypher, its Barrett's esophagus test. The case is that this test can grow fast enough to offset softer dermatology volume. The fourth-quarter report, expected around 26 February 2027, settles it. A Medicare pricing decision expected in early December comes first.

The 5 November 2026 earnings call added detail the release left out. Finsee's review of the call reports that management held the 50–52% TissueCypher target. Management also cut the 2026 DecisionDx-Melanoma volume outlook to mid-single-digit growth, from mid-to-high single digits. Finsee calculates that the guidance midpoint implies fourth-quarter revenue of about $99.9 million, below Q3's $102.9 million, with flat average selling prices assumed.

The market has priced the raise and is weighing the melanoma cut. The shares closed at $32.52 on 6 November 2026, the first session after the report, against $34.20 on 5 November 2026, and closed at $33.99 on 11 November 2026. Analysts moved the other way: KeyBanc raised its target to $40 on 6 November 2026 and Baird to $41 on 9 November 2026, per Benzinga.

Bullish and bearish views on Castle Biosciences, Inc.

The bull case on Castle Biosciences, Inc. (CSTL), in brief: third revenue guidance raise this year. The bear case: fourth-quarter TissueCypher needs a step up.

Bull case

• Third revenue guidance raise this year. Castle lifted 2026 revenue guidance to $385–395 million on 5 November 2026, from $365–375 million set on 30 July 2026. Benzinga put the pre-report consensus estimate at $373.8 million.
• Q3 beat revenue estimates. Q3 2026 net revenue was $102.9 million, up 24% from $83.0 million a year earlier, per the company's 8-K. Benzinga carried a $92.5 million estimate.
• TissueCypher plan held after a slower quarter. Q3 test reports were 15,574, up from 10,609 a year earlier and 14,988 in Q2 2026, per the company's releases. Finsee reports management kept the 50–52% full-year growth target on the call.
• Adjusted profit arrived as promised. Q3 adjusted earnings before interest, taxes, depreciation and amortization (EBITDA) were $12.7 million, up from $9.2 million, per the 8-K. Chief Financial Officer Frank Stokes said on 5 November 2026 that, absent a change in strategic direction, full-year 2027 adjusted EBITDA should be positive.
• Cash is building. Cash, cash equivalents and marketable investment securities were $277.7 million at 30 September 2026, up from $266.8 million at 30 June 2026. Q3 operating cash flow was $19.7 million.
• New melanoma data support the core dermatology test. In a 750-patient study of thin T1a melanomas presented at the Society of Dermatology Physician Associates fall conference (11 November 2026 to 15), DecisionDx-Melanoma flagged 88 patients (about 12%) as higher risk, per Castle's 11 November 2026 release. Five-year melanoma-specific survival was 97.1% for the lowest-risk class against 86.2% for the highest.
• Two target raises after the report. KeyBanc kept Overweight and raised its target to $40 from $35 on 6 November 2026, and Baird kept Outperform with a $41 target on 9 November 2026, per Benzinga.

Bear case

• Fourth-quarter TissueCypher needs a step up. Sequential additions slowed to 586 reports in Q3 from 3,243 in Q2, per Finsee. Finsee calculates the 51% midpoint requires about 16,604 fourth-quarter reports, roughly 1,030 more than Q3.
• Melanoma outlook was cut. DecisionDx-Melanoma reports were 10,177 in Q3, down from 10,459 a year earlier, per the 8-K. Management now expects mid-single-digit 2026 growth, per Finsee's account of the call.
• Revenue is guided down sequentially. Q3 revenue excluding prior-period items was $101.9 million, per Finsee, and the guidance midpoint implies about $99.9 million in Q4. With prices assumed flat, pricing is not expected to add revenue.
• Medicare pricing for AdvanceAD-Tx is contested. An advisory panel voted 21–0 to link the eczema test to an existing $3,675 rate, but the Centers for Medicare & Medicaid Services (CMS) proposed gap-fill pricing, per Finsee. Castle is appealing ahead of a final decision expected in early December.
• DecisionDx-SCC coverage is years out. Management assumes no restoration of Medicare coverage in 2027 and has placed it in its 2028 plan, per Finsee. Q3 SCC reports were 3,882, down from 4,186.
• GAAP results remain negative. Q3 GAAP net loss was $4.1 million, against $0.5 million a year earlier. Diluted shares were 30.6 million, up 5.4% year on year, per Finsee, alongside $11.2 million of stock-based compensation.
• Steady insider selling. Chief Executive Derek Maetzold sold 14,496 shares on each of 5 October 2026, 19 October 2026 and 2 November 2026, the last at an average $36.10, per SEC Form 4 filings. Chief Commercial Officer Tobin Juvenal sold on four dates between 29 September 2026 and 28 October 2026; all sales ran under Rule 10b5-1 plans.

Price setup

The shares closed at $33.99 on 11 November 2026, per adjusted daily closes. That sits just under the 50-day moving average of $34.30 and above the 200-day moving average of $28.24, both as of that close. The three-month change is 11.3%, measured from the $30.55 close of 13 August 2026.

The 52-week intraday high is $44.28, set on 26 January 2026, and the last close is 23.2% below it. The 52-week closing low is $18.15 on 13 May 2026. Since the Q3 report the shares have traded between the $32.52 close of 6 November 2026 and the $34.42 close of 10 November 2026. The $30.55 close of 13 August 2026 marks the start of the three-month gain; a weekly close beneath it would give that gain back. KeyBanc's $40 and Baird's $41 targets both sit below the January high.

Catalysts ahead

• 16 November 2026: Jefferies Global Healthcare Conference one-on-one meetings, 16 November 2026 to 19. Gives institutional investors private access to management in the first weeks after the Q3 report and the melanoma outlook cut.
• 18 November 2026: Company overview at the Stephens Annual Investment Conference, 12:30 p.m. Central. Public commentary shows how firmly management holds the 50–52% TissueCypher plan and the positive 2027 adjusted EBITDA expectation.
• 2 December 2026: Company presentation at the Piper Sandler 38th Annual Healthcare Conference, 8:10 a.m. Eastern. The last scheduled public management update before year end; any change to fourth-quarter TissueCypher or melanoma volume commentary would show here.
• ~4 December 2026 (est.): CMS final clinical laboratory fee schedule determinations. Settles whether AdvanceAD-Tx gets the $3,675 rate the advisory panel backed 21–0 or gap-fill pricing, which shapes the newer-test revenue contribution.
• ~26 February 2027 (est.): Fourth-quarter and full-year 2026 report. Shows whether TissueCypher reports rose above 15,574, whether full-year growth met 50–52%, and whether revenue landed inside $385–395M.

What would change the view

A weekly close below $29.00, under the $30.55 close of 13 August 2026, which would erase the three-month gain. Full-year 2026 revenue below $385 million, or fourth-quarter TissueCypher reports below Q3's 15,574, would also break the case.

The risks this note tracks, each with what would confirm it:

• TissueCypher growth slows further, removing the main driver of the commercial recovery. Confirmed by: fourth-quarter TissueCypher reports below the 15,574 of Q3 2026, or full-year 2026 growth under 50%.
• Dermatology tests keep shrinking, leaving revenue dependent on one test. Confirmed by: fourth-quarter DecisionDx-Melanoma reports below the year-earlier quarter, or full-year growth short of the mid-single-digit outlook.
• Medicare prices AdvanceAD-Tx through gap-fill, delaying a settled payment rate for the eczema test. Confirmed by: the final CMS clinical laboratory fee schedule in December keeping gap-fill pricing despite Castle's appeal.
• Positive adjusted profit fails to hold while costs absorb the revenue gains. Confirmed by: zero or negative Q4 2026 adjusted EBITDA, or a withdrawal of the positive 2027 adjusted EBITDA expectation.
• The raised revenue range proves too high with average selling prices assumed flat. Confirmed by: full-year 2026 revenue below $385M, with management citing lower average selling prices.

What it trades with

Castle trades as a small-cap diagnostics name, with moves driven by its own test volumes, payer decisions and Medicare pricing more than by broad market direction. Its exposure is to CMS fee schedule and MolDX coverage decisions, which also affect other molecular diagnostics laboratories. Small-cap healthcare sentiment and interest-rate moves affect the group, but company reports and coverage rulings have set the largest swings in these shares.