Mo. Rev. Stat. § 140.130

At every annual settlement made by a collector of the revenue after this chapter shall take effect, all delinquent real estate and delinquent personal tax lists and back tax bills for taxes on real estate and tangible personal property shall be carefully examined by the board of equalization and if there appear thereon any back tax bills which have appeared thereon for a period of five years or more which, in the opinion of a majority of said board, are too small to justify the expense of suit or foreclosure, or which are against exempt property, or which are against property which is not worth the taxes, interest and cost, and cannot be compromised as provided by law, the same shall, upon order of such board or a majority thereof, be stricken from such delinquent real estate or back tax books and the tax bills therefor shall be cancelled by the collector.