In Matter of Marin, 16 I&N Dec. 581 (BIA 1978), the immigration judge (“IJ”) found respondent deportable as charged on August 23, 1977 and denied his application for a waiver of inadmissibility under §212(c) and respondent's appeal was dismissed.
Cancellation of Removal is for LPRs who have been placed in removal proceedings. If you are in removal proceedings and are a green card holder, then this relief may be available to you. However, this is a defensive tactic that can only be filed in immigration court.
Cancellation of removal under § 240(A) provides relief for removable LPRs to retain their LPR status and avoid deportation. However, if you are an LPR and under removal proceedings, you must prove several points to attain this relief.