AnaptysBio (ANAB) - Get Report shares fell to their lowest level in two years after the biotech company released Phase II results that analysts questioned because they included only two participants.

The stock on Tuesday was down as much as 16% to a 52-week low of $29.44, before regaining some ground. The stock last traded around $31.22, down 11%. It was trading at a 52-week high of $100.49 a year ago.

SunTrust was "admittedly underwhelmed by the fact that interim data only included 2 subjects while [the] full study is expect[ed] to enroll 10 subjects," according to a Sept. 30 note from analyst Joon Lee, who has a buy recommendation and $93 target on the stock.

The company said a third patient dropped out of the study of patients with generalized pustular psoriasis early due to possible drug-related staph aureus infection.

While Lee was encouraged by parts of the study, "We are admittedly a bit disappointed by the limited scope of the data shared ... after much anticipation."

Cantor Fitzgerald analyst Ellie Merle was also "surprised" there were just two patients of data, according to a note, "but we think this was due to the washout requirement, which is now being lifted."

Merle, who has an overweight recommendation on the stock and $140 price target, also said the data show "very clear signs of activity in a very severe, difficult-to-treat population."

AnaptysBio says moderate-to-severe GPP is a chronic, life-threatening, rare inflammatory disease with no approved therapies.

A spokesperson at AnaptysBio couldn't immediately be reached for comment on the study.