 When searching for explosive riskreward plays, look no further than penny stocks. These names trading for under 5 per share are considered to be some of the most controversial on the Street, and divide market watchers into two factions: critics and fans.The former brings a valid argument to the table. Stocks dont just end up trading at such low levels; typically, theres a very real reason for their bargain price tags. This can be weak fundamentals or headwinds that are too strong to overcome.As for the latter, the potential for an investment worth only pocket change to appreciate even a seemingly insignificant amount, the result of which could be massive percentage gains, is too enticing to ignore. Not to mention the low share price means you can carve out a bigger stake for less money upfront.The implication for investors? Due diligence is essential, as some penny stocks might not have what it takes to climb their way back up.Taking all of this into consideration, we used TipRanks database to pinpoint three penny stocks in the healthcare sector with promising long-term growth prospects. Each gets a thumbs up from the analyst community, scoring a Strong Buy consensus rating, and boasts huge upside potential. We are talking returns of at least 100 over the next months.Accuray Inc. ARAYWith its cutting-edge CyberKnife S7 System, Accuray provides both practices and clinicians with the capabilities to deliver personalized stereotactic radiosurgery SRS, stereotactic body radiotherapy SBRT and hypofractionated radiotherapy treatments. Given its 2.28 share price, some believe that now is the ideal time to get on board.Cowen analyst Joshua Jennings acknowledges that COVID-19 has brought about strong headwinds for the radiation oncology space as a whole, with multiple hospitals re-prioritizing their capital equipment purchasing plans. Yet, the analysts bullish thesis on ARAY remains very much intact, with Jennings arguing that the rebound should be the focus here. He calls for sequential improvements throughout fiscal 2021.Expounding on this, Jennings stated, We believe the company is well-positioned to weather the storm and capitalize on its longer-term opportunities. ARAY has multiple attractive growth drivers that will kick back in during normalized periods. Its strategic standing in China, combined with its replacement cycle prospects and overall radiation oncology market dynamics, fuels our optimistic outlook for a sequential recovery trajectory in fiscal 2021 and the return to growth in fiscal 2022 off of a pre-COVID-19 revenue run rate.We would highlight that ARAY shares remain deeply discounted at under 0.7x forward sales and represent an attractive value proposition considering the company was on track to deliver an 8-12 revenue CAGR prior to the COVID-19 crisis, the analyst added.To this end, Jennings rates ARAY an Outperform i.e. Buy along with an 8.00 price target. Should this target be met, a twelve-month gain of 250 could be in store. To watch Jennings track record, click here Like Jennings, other analysts also take a bullish approach. ARAYs Strong Buy consensus rating breaks down into 3 Buy ratings received in the last three months. Additionally, the 8 average price target matches Jennings. See ARAY stock analysis on TipRanksZiopharm Oncology ZIOPUtilizing the bodys immune response, Ziopharm Oncology develops immuno-oncology gene and cell therapies to fight blood cancers and solid tumors. Based on its latest data readout and 3.27 share price, its no wonder this name is on Wall Streets radar.Recently, ZIOP released data on its controlled IL-12 program in monotherapy and combination in glioblastoma GBM. Writing for Cantor, 5-star analyst Alethia Young believes both the monotherapy and combination results support the promising efficacy trends that were already seen. Also encouraging, she highlights the fact that the monotherapy study survival data now fairly mature clearly support further development.Looking more closely at the survival data, in a subgroup of 20 patients that were given low-dose steroids and unifocal disease, 16.2 months of median survival were witnessed, with the mean follow up landing at 14.1 months. As Young was expecting to see mean survival come in at 6-12 months, she is optimistic about the programs potential.As for the combination portion, even though median follow was shorter than monotherapy at 8.3 months, Young pointed out, IL-12 helps put T cells into the tumor, which could create PD-1 on the surface receptor, suggesting that adding PD-1 could be synergistic by turning cold tumors little immune activity into hot ones.To sum it all up, Young commented, Refractory GBM remains an area of high unmet need. Importantly, we also think either monotherapy or combination provide shots on goal to improve the standard of care. So far, the safety has looked good in the main study as well.It should be noted that the IL-12 and GBM space has faced challenges in the past, which has contributed to the skepticism surrounding ZIOPs pipeline. However, everything that the company has going for it prompted Young to stay with the bulls. Along with an Overweight rating, she left her price target at 6. This figure implies shares could climb 83 higher in the next year. To watch Youngs track record, click here All in all, other analysts are on the same page. 4 Buys and no Holds or Sells add up to a Strong Buy consensus rating. Based on the 6.50 average price target, which is more aggressive than Youngs, the upside potential comes in at 99. See Ziopharm stock analysis on TipRanksEntasis Therapeutics ETTXLast but not least we have Entasis Therapeutics, which develops molecules that could potentially address and overcome mechanisms of antibiotic resistance in specific bacterial pathogens. Currently going for 2.98 apiece, several members of the Street believe that its share price reflects an attractive entry point.ETTX is slated to release topline data for its Phase 3 ATTACK study, which is evaluating SUL-DUR ETX2514SUL, a fixed-dose combination of the broad-spectrum beta-lactamase inhibitor ETX2514 with sulbactam, as a treatment for patients with pneumonia or bloodstream infections caused by carbapenem-resistant Acinetobacter baumannii. COVID-19 has had an impact on the studys enrollment, but Wedbush analyst Robert Driscoll remains squarely in the bull camp, pointing out that efforts have been made to limit the impact on the trial timeline.Driscoll added, We expect enrollment will be more rapid once sites China open recruitment ETTXs partner Zai Labs is co-enrolling up to 20 of the patients in ATTACK, which will likely allow for approval in China should ATTACK be successful. We believe the study has a high chance of success given demonstrated in vitro activity against a panel of Acinetobacter strains, dose proportional PK in healthy volunteers within the predicted therapeutic range, and a BAL study showing equivalent lung penetration for SUL-DUR to avibactam approved for HABP VAP in combination with ceftazidime.Along with this, Phase 2 data demonstrated SUL-DUR was generally well tolerated in cUTI patients. It also didnt produce serious adverse events, with the adverse event profile resembling the placeboIMI arm.It should be noted that the ongoing Phase 3 uncomplicated gonorrhea study has been temporarily suspended. However, Driscoll tells clients that topline data is still set for publication in 2H:21. Speaking to the potential opportunity, he said, Phase 2 data, published in NEJM, demonstrated 100 success rate for 47 urogenital gonorrhea patients treated with 3 g zoliflodacin vs. 100 patients treated with an intramuscular injection of ceftriaxone. We see a significant opportunity for ETTX given the lack of recommended oral antibiotics as an alternative to intramuscular administered ceftriaxone, which is currently the only recommended option.As the recent private placement could raise 31.7 million and extend its cash runway into the middle of 2021, Driscoll likes what hes seeing. To this end, he maintained an Outperform i.e. Buy rating along with a 7 price target, which leaves room for shares to skyrocket 135 in the next twelve months. To watch Driscolls track record, click here Do other analysts agree with Driscoll? They do. Only Buy ratings, 4, in fact, have been issued in the last three months, so the consensus rating is a Strong Buy. At 6.25, the average price target puts the potential twelve-month gain at 110. See ETTX stock-price forecast on TipRanksTo find good ideas for penny stocks trading at attractive valuations, visit TipRanks Best Stocks to Buy, a newly launched tool that unites all of TipRanks equity insights. 