Viracta Therapeutics (VIRX) S-4/A Registration of securities issued in business combination transactions (amended)

Exhibit 8.2

Wilson Sonsini Goodrich & Rosati Professional Corporation   650 Page Mill Road Palo Alto, California 94304-1050   O: 650.493.9300 F: 650.493.6811

January 12, 2021

Viracta Therapeutics, Inc.

2533 South Coast Hwy 101 #210

Cardiff, CA 92007

Ladies and Gentlemen:

We have acted as counsel to Viracta Therapeutics, Inc., a Delaware corporation (the “Company”), in connection with that certain Agreement and Plan of Merger and Reorganization, made and entered into as of November 29, 2020 (the “Agreement”), by and among Sunesis Pharmaceuticals, Inc., a Delaware corporation (“Acquiror”), Sol Merger Sub, Inc., a Delaware corporation and wholly-owned subsidiary of Acquiror (“Merger Sub”), and the Company, pursuant to which Merger Sub shall be merged with and into the Company, and the separate existence of Merger Sub shall cease. The Company will continue as the surviving corporation in the Merger. This opinion is being delivered in connection with the Registration Statement (File No. 333-251567) of the Acquiror on Form S-4 filed on December 22, 2020 with the Securities and Exchange Commission, as amended and supplemented through the date hereof (the “Registration Statement”). This opinion is being rendered pursuant to the requirements of Item 21(a) of Form S-4 under the Securities Act of 1933, as amended. Capitalized terms used herein but not defined shall have the meanings set forth in the Agreement.

In preparing the opinion set forth below, we have examined and reviewed originals or copies, certified or otherwise identified to our satisfaction, of the Agreement, including the exhibits thereto, the Registration Statement, the representation letters of officers of Acquiror, Merger Sub and the Company (each a “Representation Party” and together, the “Representation Parties”) to be delivered to us for purposes of this opinion (the “Representation Letters”) and such other documents, certificates and records as we have deemed necessary or appropriate as a basis for our opinion. In our examination, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified, conformed, photostatic or electronic copies, and the authenticity of the originals of such latter documents.

In rendering our opinion, we have relied upon statements, representations, warranties and covenants of officers and other representatives of the Representation Parties, and we have assumed that such statements, representations, warranties and covenants, including those set forth in the Representation Letters, are and will continue to be true, correct and complete (and, to the extent relevant, complied with) through the effective time of the Merger without regard to any qualification as to knowledge, belief, intent, or otherwise.

In rendering our opinion, we have assumed, without any independent investigation or examination thereof, that (i) the Merger will be consummated in the manner described in the Agreement and the Registration Statement, will be effective under applicable state law, and that none of the terms or conditions contained therein will be waived or modified and (ii) the Agreement, the Registration Statement and the Representation Letters accurately and completely reflect the facts relating to the Merger. Our opinion assumes and is expressly conditioned on, among other things, the initial and continuing accuracy of the facts, information, covenants, representations and warranties set forth in the documents referred to above, including those set forth in the Representation Letters.

Viracta Therapeutics, Inc.

January 12, 2021

Page 2

Our opinion is based on the Internal Revenue Code of 1986, as amended (the “Code”), Treasury Regulations promulgated thereunder, judicial decisions, published positions of the Internal Revenue Service (the “Service”), and such other authorities as we have considered relevant, all as in effect on the date of this opinion and all of which are subject to change or differing interpretations, possibly with retroactive effect. A change in the authorities upon which our opinion is based could affect the conclusions expressed herein. Moreover, there can be no assurance that positions contrary to our opinion will not be taken by the Service or, if challenged, by a court.

Based upon the foregoing we hereby confirm that, subject to the assumptions, exceptions, limitations and qualifications set forth herein and therein, the disclosure contained in the Registration Statement under the heading “Material U.S. Federal Income Tax Consequences of the Merger,” constitutes our opinion as to the material U.S. federal income tax consequences of the Merger to beneficial owners of Company capital stock that receive Acquiror common stock pursuant to the Merger.

Except as expressly set forth above, we express no other opinion. This opinion has been prepared solely in connection with the Registration Statement and may not be relied upon for any other purpose without our prior written consent.

This opinion is expressed as of the date hereof, and we are under no obligation to supplement or revise our opinion to reflect any legal developments, any factual matters arising subsequent to the date hereof, or the impact of any information, document, certificate, record, statement, representation, covenant, or assumption relied upon herein that becomes incorrect or untrue.

In accordance with the requirements of Item 601(b)(23) of Regulation S-K under the Securities Act of 1933, as amended (the “Securities Act”), we hereby consent to the filing of this opinion as an exhibit to the Registration Statement. In giving this consent, we do not admit that we come within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Securities Exchange Commission (the “SEC”) thereunder, nor do we admit that we are experts with respect to any part of the Registration Statement within the meaning of the term “experts” as used in the Securities Act or the rules and regulations of the SEC thereunder.

Very truly yours,

/s/ Wilson Sonsini Goodrich & Rosati, P.C.

WILSON SONSINI GOODRICH & ROSATI

Professional Corporation