X0306 4 2021-12-16 0 0000882361 Aptose Biosciences Inc. APTO 0001275087 PLATZER ERICH C/O APTOSE BIOSCIENCES INC. 251 CONSUMERS ROAD, SUITE 1105 TORONTO A6 M2J 4R3 ONTARIO, CANADA 1 0 0 0 Common Shares 2021-12-16 4 P 0 50000 1.37 A 455000 D Common Shares 2021-12-16 4 P 0 30000 1.38 A 485000 D Common Shares 2021-12-16 4 P 0 20000 1.40 A 505000 D The price reported in Column 4 is a weighted average price. The shares were purchased in multiple transactions at prices ranging from $1.365 to $1.39, inclusive. The reporting person undertakes to provide to Aptose Biosciences Inc., any security holder of Aptose Biosciences Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth above. The price reported in Column 4 is a weighted average price. The shares were purchased in multiple transactions at prices ranging from $1.395 to $1.40, inclusive. The reporting person undertakes to provide to Aptose Biosciences Inc., any security holder of Aptose Biosciences Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth above. /s/ Janet Clennett as attorney-in-fact for Erich Platzer 2021-12-17