Not every pharmaceutical company is flocking to East Cambridge.

Deciphera Pharmaceuticals is amending its 44K SF lease at Anchor Line Partners’ Post at 200 Smith to take an additional 38K SF and make the Waltham development its new headquarters, according to an April 29 filing with the Securities and Exchange Commission.

Its current headquarters is at Boston Properties’ CityPoint less than 2 miles away, also in Waltham.

JLL Managing Director Matt Daniels, who represented Deciphera Pharmaceuticals, confirmed the move. Deciphera and Anchor Line Partners did not respond to requests for comment in time for publication.

The pharmaceutical company signed its initial lease last year, with Anchor Line covering $2.7M in build-out costs, Bisnow first reported. The expansion brings Deciphera’s Post at 200 Smith footprint to just over 82K SF. Work is still underway building out the first phase of Deciphera’s new headquarters.

Deciphera will pay $49/SF for the expanded area, and Anchor Line is offering as much as $2.28M in build-out costs, according to the SEC filing. The pharmaceutical company had a right of first offer on the space in its original lease.

Post at 200 Smith had been a rare instance of speculative development along the Route 128 corridor this cycle. Most development has been build-to-suit, as suburban tenants like PTC have migrated toward downtown Boston.

But developers may be warming up to more spec projects, as Hobbs Brook is planning more than 500K SF of spec office and lab development near Post at 200 Smith. Other developers have pitched the corridor as a relief valve to tenants in crowded submarkets like Kendall Square as they have added urbanized amenities.

“It’s not surprising to see the Waltham market excel in an age of urbanization,” Perry Director of Intelligence Brendan Carroll said. “The success of 200 Smith should lend confidence to Hobbs Brook and others eyeing Waltham speculative projects.”