13G Filing: Foresite Capital Fund III, L.P. and Tocagen Inc (TOCA)

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Schedule 13G
(Rule 13d-102)

INFORMATION TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULES 13d-1 (b), (c) AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 (b)

(Amendment No. ___________)*

Tocagen Inc.

(Name of
Issuer)

Common Stock

(Title of
Class of Securities)

888846102

(CUSIP Number)

April 13, 2017

(Date of
Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to
which this Schedule is filed:

¨
Rule 13d-1(b)

x Rule
13d-1(c)

¨
Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a
reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment
containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page
shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”)
or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however,
see the Notes).

(Continued on following pages)

Page 1 of 9

Exhibit Index on Page 8