1. Nature of the Business Proteostasis Therapeutics, Inc. (the Company) was incorporated in Delaware on December 13, 2006. The Company is a clinical stage biopharmaceutical company committed to the discovery and development of novel therapeutics to treat cystic fibrosis (CF) through theratyping, or the process of matching modulators to individual response to treatment regardless of cystic fibrosis transmembrane conductance regulator (CFTR) mutations. CF is a disease caused by defects in the function or abundance of CFTR protein. Although, CF is defined as a monogenic recessive genetic disorder caused by mutations in the CFTR gene, there is a broad range of disease activity for different organ systems in CF, including lung disease, meconium ileus, diabetes, and liver disease, even for CF patients who are homozygous for the most common mutation, F508del mutation. In summary, CF genotype does not always match CF phenotype. Since its inception, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, acquiring and developing product and technology rights, and conducting research and development activities. It has funded its operations to date with proceeds from the sale of preferred stock, the issuance of convertible promissory notes, proceeds from its initial public offering in February 2016, proceeds from its follow-on public offerings, and payments received in connection with collaboration agreements and a research grant, as well as funds from the sale of stock under the at-the-market offering program described below. The Company does not have any products approved for sale and has not generated any revenue from product sales. The Company has not generated any commercial revenue since inception. As a result, the Company has incurred recurring losses and requires significant cash resources to execute its business plans. In accordance with ASC 205-40, Going Concern (ASC 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Companys ability to continue as a going concern within one year after the date the financial statements are issued . As of June 30, 2020, the Company had an accumulated deficit of $355.4 million. The Company has incurred losses and negative cash flows from operations since its inception. During the six months ended June 30, 2020, the Company incurred losses of $18.8 million and used $21.4 million of cash in operations. The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. The Company currently expects that its cash, cash equivalents and short-term investments of $48.9 million will be sufficient to fund its operating expenses and capital requirements, based upon its current operating plan, for at least 12 months from the date that these financial statements are issued. The Company will require additional funding to fund its proposed Phase 3 Modulator Options to RestorE CFTR (MORE) trial, its CHOICES program, and to advance its proprietary combination therapy candidates through regulatory approval and into commercialization, if approved. Accordingly, the Company is in the process of considering various financing alternatives to support its operating and capital needs, including public or private equity or debt financings, third-party funding, marketing and distribution arrangements, as well as other collaborations, strategic alliances and licensing arrangements, or any combination of these approaches. The Company is also considering strategic alternatives for its CF portfolio, including its proprietary combination therapy candidates posenacaftor, dirocaftor, and nesolicaftor, with the goal of maximizing stockholder value of these assets. However, the Company does not currently have any commitments for future external funding and additional financing may not be available on a timely basis, on acceptable terms, or at all. The novel coronavirus (COVID-19) pandemic continues to rapidly evolve and has already resulted in a significant disruption of global financial markets. If the disruption persists and deepens, the Company could experience an inability to access additional capital, when and if needed. If the Company is unable to implement any strategic or financing alternative and adequate funds are not available in the future, the Company may be required to delay, limit, reduce or terminate its clinical development or future commercialization efforts or obtain funds through arrangements with collaborators or others that may require it to relinquish rights to develop and market product candidates that it would otherwise prefer to develop and market themselves.