X0306 4 2019-07-29 0001447362 CASTLE BIOSCIENCES INC CSTL 0001783292 MGC Venture Partners 2013 GP, LLC C/O MOUNTAIN GROUP CAPITAL, LLC 3835 CLEGHORN AVE., SUITE 300 NASHVILLE TN 37215 true 0001572764 MGC Venture Partners 2013, L.P. C/O MOUNTAIN GROUP CAPITAL, LLC 3835 CLEGHORN AVE., SUITE 300 NASHVILLE TN 37215 true 0001783291 MGC Venture Partners 2018 GP, LLC C/O MOUNTAIN GROUP CAPITAL, LLC 3835 CLEGHORN AVE., SUITE 300 NASHVILLE TN 37215 true 0001745133 MGC VENTURE PARTNERS 2018, L.P. C/O MOUNTAIN GROUP CAPITAL, LLC 3835 CLEGHORN AVE., STE. 300 NASHVILLE TN 37215 true 0001749814 MGC VENTURE PARTNERS QP 2018, L.P. C/O MOUNTAIN GROUP CAPITAL, LLC 3835 CLEGHORN AVE., STE. 300 NASHVILLE TN 37215 true Common Stock 2019-07-29 4 C 0 1336927 A 1336927 I See footnotes Common Stock 2019-07-29 4 C 0 97428 12.8 A 1434355 I See footnotes Common Stock 2019-07-29 4 P 0 62500 16 A 1496855 I See footnotes Common Stock 2019-07-29 4 P 0 115300 16 A 115300 I See footnotes Common Stock 2019-07-29 4 P 0 134700 16 A 134700 I See footnotes Series A Preferred Stock 2019-07-29 4 C 0 19524 D CommonStock 16015 0 I See footnotes Series D Preferred Stock 2019-07-29 4 C 0 337754 D CommonStock 277074 0 I See footnotes Series E-1 Preferred Stock 2019-07-29 4 C 0 463453 D CommonStock 380190 0 I See footnotes Series E-2 Preferred Stock 2019-07-29 4 C 0 158379 D CommonStock 129925 0 I See footnotes Series E-3 Preferred Stock 2019-07-29 4 C 0 142843 D CommonStock 117180 0 I See footnotes Series F Preferred Stock 2019-07-29 4 C 0 507762 D CommonStock 416537 0 I See footnotes Convertible Promissory Note 12.8 2019-07-29 4 C 0 1200000 D Common Stock 97428 0 I See footnotes The shares of Common Stock issued upon conversion of the Preferred Stock were calculated by first aggregating all series of Preferred Stock held by MGC Venture Partners 2013, L.P. ("MGC 2013 LP"), in accordance with the terms of the then-effective Certificate of Incorporation of Castle Biosciences, Inc. (the "Issuer"). Every 1.219 outstanding shares of Preferred Stock automatically converted into 1 share of Common Stock immediately prior to the closing of the Issuer's initial public offering (the "IPO"), for no additional consideration, with cash paid for any fractional shares. The Preferred Stock had no expiration date. Held directly by MGC 2013 LP. MGC Venture Partners 2013 GP, LLC ("MGC 2013 GP") is the general partner of MGC 2013 LP. MGC Venture Partners 2018 GP, LLC ("MGC 2018 GP") is the general partner of MGC Venture Partners 2018, L.P. ("MGC 2018 LP") and MGC Venture Partners QP 2018, L.P. ("MGC QP 2018 LP"). Each of MGC 2013 LP, MGC 2013 GP, MGC 2018 LP, MGC QP 2018 LP and MGC 2018 GP directly (whether through ownership or position) or indirectly through one or more intermediaries, may be deemed for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, to be the indirect beneficial owner of some or all of the shares owned by MGC 2013 LP, MGC 2018 LP and MGC QP 2018 LP and, therefore, a "ten percent holder" hereunder. Each of Joseph C. Cook, Jr., Joseph C. Cook III, Steven D. Singleton and Byron W. Smith are managing directors of MGC 2013 GP and share voting and investment power over the shares held by MGC 2013 LP. Each of Joseph C. Cook, Jr., Joseph C. Cook III, Steven D. Singleton, Byron W. Smith, Jay Ferguson and Rob Readnour are managing partners of MGC 2018 GP and share voting and investment power over the shares held by MGC 2018 LP and MGC QP 2018 LP. Each of the Reporting Persons disclaims beneficial ownership of the shares held by any other Reporting Persons reported herein, except to the extent of its pecuniary interest therein, and this report shall not be deemed an admission that the Reporting Persons are the beneficial owners of such securities for purposes of Section 16 or for any other purposes. The principal amount of the Convertible Promissory Note held by the designated Reporting Person was $1,200,000.00. Upon closing of the IPO, all unpaid principal and accrued interest outstanding on the Convertible Promissory Note (the "Conversion Amount") automatically converted into the number of shares of Common Stock equal to the Conversion Amount as of the date immediately prior to the closing date divided by 80% of the IPO price per share of $16.00 per share. Represents a purchase from the underwriters in the Issuer's IPO. Held directly by MGC 2018 LP. Held directly by MGC QP 2018 LP. /s/ Byron W. Smith, Managing Member 2013 GP, LLC, the General Partner of MGC Venture Partners 2013, L.P. 2019-07-29 /s/ Byron W. Smith, Managing Member of MGC Venture Partners 2013 GP, LLC 2019-07-29 /s/ Jason S. Ferguson, Managing Partner of MGC Venture Partners 2018 GP, LLC, the General Partner of MGC Venture Partners 2018, L.P. 2019-07-29 /s/ Jason S. Ferguson, Managing Partner of MGC Venture Partners 2018 GP, LLC, the General Partner of MGC Venture Partners QP 2018, L.P. 2019-07-29 /s/ Jason S. Ferguson, Managing Partner of MGC Venture Partners 2018 GP, LLC 2019-07-29