Company: CSTL
Filing Date: 2025-11-03
Form Type: S-8
Source: 0001628280-25-048270
Chunk: 0

Company: CASTLE BIOSCIENCES INC
Filing Date: 2025-11-03
Form: S-8
Chunk 0
---
<div align='center'>As filed with the Securities and Exchange Commission on November 3, 2025</div>

#### Registration No. 333-

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

#### FORM S-8

### REGISTRATION STATEMENT

#### UNDER

#### THE SECURITIES ACT OF 1933

#### Castle Biosciences, Inc.
<div align='center'>(Exact name of registrant as specified in its charter)</div>

| Delaware                                 |     |         77-0701774 |
| (State or other jurisdiction of          
 incorporation or organization)           |     |   -I.R.S. Employer 
 Identification No. |
| 505 S. Friendswood Drive, Suite 401      
 Friendswood, Texas                       |     |              77546 |
| (Address of Principal Executive Offices) |     |          -Zip Code |

#### Castle Biosciences, Inc. 2022 Inducement Plan
<div align='center'>(Full titles of the plans)</div>

#### Derek J. Maetzold

#### President and Chief Executive Officer

#### Castle Biosciences, Inc.

#### 505 S. Friendswood Drive, Suite 401

#### Friendswood, Texas 77546
<div align='center'>(866) 788-9007

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:</div>

| Thomas A. Coll, Esq.        
 Carlos Ramirez, Esq.        
 Cooley LLP                  
 10265 Science Center Drive  
 San Diego, California 92121 
 (858) 550-6000              |

Indicate by check mark whether the Registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

| Large accelerated filer |     | o |     | Accelerated filer         |     | x |
| Non-accelerated filer   |     | o |     | Smaller reporting company |     | o |
| Emerging growth company |     | o |     |                           |     |   |

If an emerging growth company, indicate by check mark if the