HENDERSON, Nev. ( TheStreet) -- Spectrum Pharmaceuticals' ( SPPI - Get Report) colon cancer drug Fusilev could report a mega-blowout quarter. Fusilev sales totaled $49.7 million in June, according to monthly sales data from Wolters Kluwer released late Tuesday. That means in June alone, Spectrum sold almost as much Fusilev as the $51 million recorded in the entire first quarter. Spectrum won't announce second-quarter results until July 30, but Fusilev sales could top $90 million based on Wolters Kluwer monthly sales data, which have so far tracked accurately with actual, end-of-quarter reported sales. Fusilev sales totaled $24.8 million in May and $22.3 million in April, according to Wolters Kluwer. Spectrum continues to benefit from a shortage of generic leucovorin but now it seems doctors, particularly those in large oncology group practices, have turned to Fusilev as a permanent replacement for their colon cancer treatment regimens. The predicted reversal in Fusilev sales growth has not materialized, even with leucovorin supply shortfalls easing somewhat. Instead, Fusilev sales continue to grow month over month with no sign of stopping. Spectrum shares closed Tuesday at $15.63. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: firstname.lastname@example.org. Follow TheStreet on Twitter and become a fan on Facebook.