Table 1. . Themes, subthemes and exemplar quotations from the breast, melanoma and thoracic oncology clinician participants.

Theme 1: Varied definitions of precision oncology exist
[Precision oncology is…] Defined by patients as tailored treatment	“I think we tend to think of precision oncology in terms of genetics, but I do think that at least patients may think beyond that. I mean, it’s individualizing care to the patient…” – Melanoma
[Precision oncology is a…] Term that can be used broadly, or precisely, along a continuum of specificity	“I think one way of looking at it could be a broader, just sort of the right treatment for the right patient, and part of that is biomarker driven, but it could be broader than that.” – Breast
[Precision oncology…] Encompasses a variety of treatment options	“I think from a radiation oncology perspective as well as the surgery perspective, our treatments have become more precise as well. We really have made technological advances. I’m not sure that’s what you’re referring to when you talk about precision oncology.” – Thoracic
[Precision oncology is the…] Application of new approaches to existing goals	“Tailor treatment for what it looks like under the microscope. So we, so now we think of it more that we’re adding what – besides histologically it looks like, is genetically just another level, and we’re also sort of implied in that is that we’re expecting to have that result in a pretty high response rate, if we have hit the right group, but as I said, we’ve always done that. When I was a medical student, if you look down at the microscope and it looked like Hodgkin’s disease, you had a treatment for that that had a high response rate. So now we take it one step further by saying we have genetics.” – Melanoma
[Precision oncology means…] Using genomics as an additional source of data to guide treatment decisions	“So if I had to use that term, I would honestly I would really limit it at this point in 2019 to decisions based on genetic somatic mutations.” – Melanoma
[Precision oncology means…] Harnessing specific genomic alterations as the target or mechanism of action for precision treatments	“Right, some ALK thing, or I’m specifically choosing chemo over some – platinum chemo over a fancy thing because they have a BRCA mutation, or I’m getting a PARP inhibitor because there are BRCA mutations.” – Melanoma
[Precision oncology is…] Synonymous with personalized medicine	“Now there’s a lot more variety and its more individualized…” – Thoracic
[Precision oncology is…] A marketing term	“I feel like it’s still a lot of hype and more PR than it is med-onc or surg-onc.” – Melanoma

Theme 2: Clinicians and patients face unique challenges to precision oncology implementation
Challenges encountered by clinicians	“And so, the expectation of the clinician, the time to prepare for that client visit has just grown exponentially, and I’m not sure that we have yet to build that into our workflows.” – Breast “It’s taking the extra time, making sure that you’re not burning bridges, you’re not precluding them from entering on clinical trials in the future that may be or may not be open. It’s navigating clinical trials outside of our institution. What is best for you today without preventing you from entering promising trials in the future…. It takes a more nuanced and longer approach, and it’s a moving target. Oh, you progressed on Drug X. Now you’re asking me, what do we do next? Can I use precision medicine to determine this?” – Breast “And under that is not only that, but also having – getting tissue from outside hospitals to even test it… Or even delaying for a second biopsy if you didn’t get a sufficient amount the first time… In our own institution just getting our own pathologists to do the stains that we need without asking them each time.” – Melanoma
Challenges encountered by patients	“And sometimes patients don’t understand that it takes a long time sometimes to get the results. And sometimes, you did testing, and it’s not enough material. And so now you’ve waited a couple weeks to find out, and there’s not enough material.” – Thoracic “Or even, unfortunately, patients further out there that are seeing more rural communities that don’t even know that some of these treatments exist. Their oncologists don’t know that some of these treatments exist.” – Melanoma “But I mean but do they need to be followed by, in that case, a G.I. person or a whatever, right, for whatever incidental-oma that you found. That has consequences.” – Melanoma

Theme 3: Patient communication challenges engendered or heightened by precision oncology implementation
High expectations for personalization	“Well, it makes them [patients] feel like they’re being treated as individuals.” – Melanoma
Counteracting the effects of media	“And I have to say, part of the problem is how the media portrays cancer medicine. They’ll take a case of one patient and it’ll get like, ‘breaking news, 24 hours.’ And that’s wonderful to present those kinds of cases in the research meetings to other researchers, but it’s so irresponsible when they put that out there for people who come now, seeking this one amazing…. You know, the NIH case from last year. I mean, I don’t know how many calls we must have all had, ask the patients about the N of 1 that was promoted.” – Breast
Perception of the likelihood of a cure	“I’ve seen patients come in with the idea that because you found this mutation, or they had this trial I’m eligible for this, it’s going to be a home run thing.” – Breast
Misperceptions about side effects	“So, telling them that we can know a lot more about their tumor and then tailor a treatment that’s very specific to them. A lot of patients come in and they’re like, ‘oh, I don’t want chemo, because you know it killed my aunt’.” – Thoracic
Aligning expectations with the realities of clinical trials	“We were actually having a conversation just recently about, and I completely support clinical trials, but you reach a point where our patients have so much hope in the investigational, and they may be in the third-line setting and haven’t yet had something with known benefit. And you’re worried. You see their performance status kind of declining and they’re sacrificing so much out of their everyday and their lives, hoping that there’s the magic drug that’s investigational that’s really not proven yet. You kind of struggle.” – Breast
Treatment outcomes are individualized and not necessarily predictable	“I can also say that [colleague] here has a number of groups for the metastatic patients, younger, older. Or, the patient comes in and they’ve been on a trial or on a regimen for a long time, and they’re doing exceedingly well. Another one doesn’t do well, and you see responses vary among each other. That gives you a better understanding of how these drugs may or may not work in various individuals. It gives you hope. Oh my gosh, she’s progressed on five regimens and now she’s been well for the past year or two. And that allows patients to realize it’s not uniform, it’s different, depending on the individual. And I’m hopeful that I will be one that responds for a long time.” – Breast
Clarifying the range of possible treatment options	“If I tell people, I don’t know, I guess this is a little bit off topic, but in second-line or third-line therapy in melanoma, that’s really where we’re still in the wilderness, obviously, and if I tell them my rationale in some way is well because you had absolutely no toxicity to Ipi Nivo or response, that’s why I’m kind of thinking that maybe you do need like an injectable, or you do need something to force the T-cells that – and sometimes they just really like the idea that you’re thinking about their specific journey, and saying well, I’ve got five second-line, third-line trials there. They all have a response rate in the zero to 15% range and honestly, this is the one that has a slot open, which really is sometimes how you do it.” – Melanoma
Sometimes precision treatments are not available	“I think the biggest limitation of precision oncology, more broadly, is that unfortunately, the results don’t frequently lead to treatments that will improve outcomes and that’s where I think the disconnect is.” – Breast
Options and outcomes can be better than patients expect	“It’s a lot easier to talk to them when we say, okay well, not everybody gets chemotherapy now. There are other treatments that are available. It depends on the IMPACT [institutional tumor-germline sequencing test] of your tumor. So that makes it a lot easier.” – Thoracic
Managing disappointment and anger	“I mean, you get reports back and there’s nothing to do with it. And it’s a short conversation and the patient’s been waiting for a few weeks, and they’re hopeful. And then, their bubble is burst and then you move on, and you talk about other treatment options.” – Breast

Theme 4: Clinician communication solutions and training needs
Communicating uncertainty	“And I think all of us, to some degree, have a discomfort with uncertainty, but that I think for me starting out in fellowship that was one of the more difficult conversations to have with patients was when we – if you know the answer, even if it’s not an answer you like, we’ve all had [training] on how to give bad news since day one of medical school, but uncertainty is something that even though our research is advancing us, we’re actually, I think finding more uncertainty, not less.” – Melanoma
Communicating rationale for treatment selection	“So, when you think about communication strategies that we project or that we employ, I mean, I think it’s important to say well, there really is no biomarker for CDK4 response, although we would like it, or for MTOR response. But we do have some for PI3 kinase. So, there is level setting. And so, while they may come in with certain preconceptions, they want to go out better.” – Breast
Assessing patient knowledge and information preferences	“Or their preconceived opinions about things. So, I’m thinking about, particularly the adjuvant conversation, you know, when you put your head on the pillow at night, are you the person who needs to know you did absolutely everything, or are you the person who is going to be really upset that you got a toxicity, and maybe no benefit?… And that’s something that I have found myself saying later in the conversation and realizing that I should have said earlier in the beginning, and framed the conversation around that, as opposed to the other way around.” – Melanoma