CAMBRIDGE, Mass. ( TheStreet) -- Ariad Pharmaceuticals ( ARIA) is an interesting stock because its leukemia drug Iclusig offers plenty of gristle to both bears and bulls. Despite a relatively successful commercial launch, many investors remain unconvinced about Iclusig's potential to become a blockbuster cancer drug for Ariad. Flattening growth in the number of Iclusig prescriptions written is only adding to the debate over the drug. Ariad bears see waning Iclusig prescriptions as an early warning signal; Ariad bulls counter that this is just a natural progression of a new drug launch. Through all the noise, Ariad stands a good chance of turning Iclusig into a blockbuster drug. To get there, the company must successfully climb three walls of worry in the short, medium and long term. Ariad reports second-quarter results on August 7, with analysts, on average, expecting $10.3 million in Iclusig sales. Weekly prescription data, however, suggest June quarter sales could come in closer to $15 million. Despite the potential for a significant sales beat in the second quarter, Iclusig sales in the third quarter appear to have slowed. According to Symphony Health, new Iclusig prescriptions peaked at 62 for week ended June 7, and have since steadily fell to 29 new prescriptions two weeks ago followed by a rise to 41 new prescriptions last week. While the number of new Iclusig prescriptions is on the downtrend, the total number of prescriptions written for the drug each week has held up fairly well. To a certain extent, the divergence between new and total prescriptions is expected as a drug launch matures. In the beginning, new prescriptions are a majority of the total but as patients go back for refills, the share of new prescriptions to total prescriptions decreases. In recent weeks, new Iclusig prescriptions have fallen to about 30 percent of total prescriptions, which is in line with both Sprycel and Tasigna, two competing leukemia drugs marketed by Bristol-Myers Squibb ( BMY) and Novartis ( NVS), respectively. Investors are forward looking, so better-than-expected Iclusig sales for the second quarter won't mean as much if worries mount about Ariad's ability to meet or exceed Iclusig sales expectations for the third quarter or full year.